I’m assuming it was the norm or at least, commonplace. Along with that, how much did that culture transplant to Romans? Were ancient Greek women likewise bisexual? When did the norm die out (or did it?)
If it were really all that common, I don’t think Lysistrata could have been written.
That’s a big assumption, is it based on movies or TV?
A friend of mine told me that the Greeks considered women “inferior” and only good for procreation. If you wanted to make love to an equal, a guy was the way to go.
Greek homosexuality regularly took the form of pederasty, in which case you’d definitely not be the social equal of your partner.
There is a brilliant German comic book out there by Ralf König, also called “Lysistrata”, where the (few) gays in Athens use this situation to turn all the males into homosexuals.
Wickedly funny! 
Sexuality wasn’t viewed the same way in the Ancient World, and in fact hasn’t been viewed statically at all throughout history. Then as now most people had a preference for the opposite sex, there’s no historical evidence that this has ever been untrue or that the ~5-10% of the population we have today that is not heterosexual is especially small compared to the past.
However the reality is stimulation of the human genitals in various ways, be it sex or other forms of sexual play/touching/massage whatever is physically pleasurable, whether it be a man doing it to you or a woman. In the past essentially what it comes down to is while most people would not identify as being primarily interested in the same sex, they were more of the mind of “if I want to get my rocks off I’m not super picky about it being with the same sex.” I think a lot of the aversion/disgusts heterosexuals feel toward even the thought of say, a man stimulating their penis is built on generations and generations of cultural stigmatizing. I’m not saying I think the default human sexuality is pansexuality, but I think that while most people are what we’d think of as heterosexual, without the cultural elements I think even people who much prefer opposite sex pairings would be more open to same sex engagements.
So all that being said, in Greece and Ancient Rome many men took advantage, to be frank, of younger men and used them for sexual pleasure. That is the primary sort of relationship that occurred between primarily heterosexual Greeks and Romans and other men, an older, more powerful man basically get to have sex with a younger, less powerful (politically) man.
In both cultures it was also viewed differently based on circumstance. A young boy getting it from an older mentor didn’t get a lot of “shame” over it, as it was common place. But for an adult male to be receptive to homosexual sex, that did make him lesser / weaker. In both Greece and Rome for an adult man of position to be on the receiving end of gay sex carried with it negative cultural connotations. Also as a side note in Rome at least, there was a huge stigma against oral sex but not against anal sex. One of the worst insults in Ancient Rome was to refer to a man or a woman as someone who gives oral sex, it was seen as a deeply disgusting/abhorrent practice in any configuration (male/male, male/female.)
In both Greek and Rome a man who insisted on exclusively having sex with other men would not be received with open arms. Families had to marry off sons and sire new generations, and not participating in that would alienate you, further even in Rome/Greece where leading men had often had gay sex many many times in their lives there was still a stigma about men who solely were interesting in other men.
I also don’t mean to use Greek/Roman interchangeably, but on this subject they do have a good bit in common and in popular perception they are often associated in this way. Some differences I know of is the Greeks emphasized much deeper “emotional” relationships between males to the detriment of relationships with women. Greek women were often seen by the men as little more than brood mares, not worthy of even talking to and certainly not desirable to be seen out of the house. Roman women tended to have more political relevance, more of a place in the home and etc.
That’s about half right, at least for most of the Greek states. The ancient Greeks were deeply misogynistic, and the idea that women existed pretty much exclusively to keep house and be pregnant was widespread. However, the idea of wanting to “make love to an equal” was almost exactly the opposite of how the Greeks viewed sex. Greek sexuality wasn’t divided along straight/gay lines, it was divided along “you put your dick in someone” v. “someone puts their dick in you” lines. And being in the second group was considered to be not a good thing.
Basically, if you let someone fuck you, you were acting like a woman. An adult Greek citizen would, as a general rule, never submit to being the receptive partner in a homosexual encounter. The closest thing the Greeks had to our modern concept of a homosexual relationship would be between a slave-owner (who would always be the top) and his male slave. This sort of relationship would generally be considered unexceptional, so long as the citizen also had a wife and a few kids - it was part of every citizen’s civic duty to provide the next generation of Greeks. A citizen who wasn’t raising a family by a certain age would be viewed as an irresponsible wastrel. Whether he was shirking his family obligations in favor of fucking female prostitutes or male slaves didn’t make too much of a difference, socially.
Which brings us to the OP’s question: were ancient Greek men bisexual? Depending on how you define “bisexual,” either they almost all were, or almost none of them were. If you define “bisexual” as “sexually attracted to both genders in roughly equal measure,” then very few Greeks were bisexual. If you define it as “ever had sex with someone their own gender,” on the other hand, probably most of them were.
The concept of sexuality as identity is a very modern invention. That’s not to say that there weren’t gay people before the 19th century - the percentage of humans who are predisposed to exclusive sexual attraction to their own gender is probably fairly consistent across most cultures and eras. But such a person would not identify as “gay,” nor would the majority of the people around him identify as “straight.” It simply wasn’t part of their self-identity. A consequence of this was that sexual acts that fell outside their normal attractions weren’t a threat to their self-identity. And sexual attraction isn’t always a necessary part of sexual activity. Think how many guys you’ve known who were willing to have sex with a woman they considered unattractive, because hey, it’s still sex, right? To an ancient Greek, fucking a slave would be more or less the equivalent of fucking an ugly girl. You just close your eyes, think of that hot dancer you saw in the forum last week, and let friction do the work for you.
From what I’ve heard (sorry, no cite), Julius Caesar was an exception to this. He was notoriously anally receptive to other men.
Oh, snap! The “Queen of Bithynia” thing?
Let me guess: Not much of a supporter of Caesar, are you?
Yeah, in a nutshell, the ancient Greeks and Romans defined sexuality as ‘penetrator/penetrated’. Adult male freeborn people were penetrators, everyone else was at least ‘at risk’ of being penetrated. Being penetrated was weak/womanly/inferior/associated with slavery and a whole complex of negative images.
Also, for a man to perform cunnilingus was frankly deviant.
I doubt most ancient Greek or Roman men thought much about the idea of female homosexuality at all, though there was definitely discussion of it (as deviant, and confusing the whole penetration matrix).
The male body was ‘default’ and the standard of beauty; Aristotle’s view that women’s bodies were ‘defective’ male bodies was widespread. Most ancient Greeks also believed that the semen contained all the ‘genetic’ material, and women were only incubators for babies.
A few points:
Concerning ancient Greek misogyny in general: Yeah, that is definitely a thing, and it’s so thick and pungent that you could sell it in a cheese shop. On the other hand, though, Greek drama is chock full of strong female characters. Not just the women in Lysistrata, who have a certain power over men, but, you know, just straight up strong female characters, like Clytemnestra, Antigone and Medea. If every Greek woman was barefoot and pregnant, you have to wonder where the dramatists got their models for these characters from. On the third hand, though, these characters were played by men, since actual women weren’t allowed near a stage. So there’s that.
About female homosexuality: Yeah, the Greeks don’t seem to be all that interested in the subject, and to the extent that they are, they mostly don’t seem to think of it as particularly acceptable. It is mentioned, though, along with male/female and male/male relationships, in the wonderful speech put into the mouth of Aristophanes by Plato in the Symposium (everyone go read it now, it’s wonderful). There, at least, it doesn’t seem to be portrayed as deviant, but just as, well, a thing:
That speech, though, spends most of its time praising man-on-man love, and the men who love men as the most manly. Although, anyway, it’s not really clear how much of an oddball or otherwise Aristophanes-according-to-Plato is meant to sound like.
Well, maybe, although this really sounds like the kind of nonsense that you have to be a philosopher to argue yourself into believing (there’s a lot of that going on with Aristotle). I don’t have proof, but I suspect that any Greek who had ever noticed that children could sometimes look a lot like their mothers knew better.
Or, maybe that’s a positive because it would make him the one Emperor that the people can really get behind.
Why would you assume that?
I assume because the purported affair with Nicomedes IV was a slander leveled at Caesar by his enemies. True or not, it was considered an assault on his character as explained above by several posters.
The other thing about ancient Greek culture that contributed to the whole thing is that was a lot of gender segregation, especially among the upper classes. Women, especially upper class women, didn’t go out in public unveiled or unchaperoned, or ideally, didn’t go out at all, and for well to do Greeks, at least, there wasn’t much opportunity to get to know people of the opposite sex you weren’t related to. Part of me wonders if some of it is that Greek men didn’t have much opportunity to have sex with women.
The impression I got from reading Aristotle (and this was a 1949 edition, so I had to read between the lines) was that true love was between young men, but as you aged you had to get married and switch over to heterosexuality of the more or less traditional variety to propagate the race.
You apparently don’t know me very well.
No one has done a Wiki link yet? Oh, well. Greek pederasty: Common and sometimes institutionalized, as explained upthread.
Although, in reality, I suspect that we probably need to be careful with the broad brush. Matters of the heart are always complicated in the real world, you know? All I’m saying is, one should be wary of generalizing too much from vase paintings, philosophers, poets, Hollywood movies or Internet porn. And with Aristotle, as I mentioned, well, the usual caveats apply.
The “propagate the race” thing is interesting, though. Yeah, you are expected to do that. Also, generally, the Greeks are really not into abstinence. The matter of liking boys or girls is one thing, but the character who comes across as the biggest sexual weirdo in Greek literature is probably Hippolytus. Why? Well, firstly for worshiping Artemis as his favorite divinity, which is a girly thing to do, and thereby confusing gender boundaries. But mostly for being chaste. This pisses Aphrodite off something fierce, causing hijinks and tragedy to ensue.
The play is also a warning about an excess of lust, the opposite problem, which is Phaedra’s issue. Point, is: Middle ground seems to be the way to go, really. Otherwise, boy howdy, the Gods will mess with you.
But now I’m really digressing…
Then stop saying he liked being buggered by other men? 
As explained above, the insult isn’t the homosexuality part, as much as the “receptive” part.
Also, a general point: Yeah, the ancients got up to all sorts of things in the sack, and they sure as heck weren’t always shy about it. But you still have to take some care not to put your foot in your mouth when talking about these things. A lot of stories are meant as insults.
Take the Roman incest thing. There are stories about Roman Emperors and others going to bed with close family members. Thing is, though, this is the kind of story that a historian tells about someone he doesn’t like. You’ll hear that about a Caligula (and his sister) or a Nero (and his mother).
Which is why that scene in HBO’s *Rome *series, where it is in implied that Octavian did some naughty business with his sister Octavia, made Romans everywhere fall off their chairs. Woop-tee-doo, HBO’s Rome, you just insulted the future Emperor Augustus. I could be wrong, but I don’t really think that was the tone you were going for. I mean, it’s one thing to joke about Clinton being a womanizer, but if you throw accusations of cheating at Obama, you’d better have a good reason to, and be ready to take it outside. I mean, it’s that sort of thing. Only worse.
Whereas Marcus Antonius always wanted to be the top:
“Friends, Romans, Countrymen, lend me your rears!”