No. It’s either tuxes or tuxtopodes. Both are correct. Never tuxtopi.
Not if it’s an evening wedding, morning dress should never be worn after 5pm (neither should black tie be worn in daytime). 
I once showed up at a friend’s wedding in a suit (blue suit, red tie); I had had some job-related thing earlier and neglected to change. Everyone mocked me for trying to upstage the groom.
I come from a very casual dress culture. That was nine years ago, and I haven’t worn a suit since.
Some people will actually put in place a dress code for a wedding and reception. Ex. all men must wear tuxes.
Others have none but then you run the risk of your BIL showing up in jeans and a tank top. If your cool with that ok. But to me if I’m paying $50 a person for a reception a guest better dress nice.
I’m for everyone attending a wedding, including the bride, groom and wedding party, having to randomly exchange at least two pieces of clothing.
Having attended weddings where some of the guests looked like a muffin wrapped in a rhinestoned tutu, I am very much not!
Just out of curiosity, who came up with these rules and who really cares?
I’m not being snarky, and I do believe one’s attire should be appropriate (e.g., don’t come to a cathedral wedding in a tube top and thong) but who declared what color tie one can wear when or where? (It reminds me of an HOA run amok - they don’t just say you need to mow your yard weekly, they say it can’t be over 2.75" tall.)
Based on some of the things I’ve read here, I expect I’ve been mocked behind my back for years.
Quick story, the president of the Applebee’s restaurant chains daughter was getting married and they had this big fancy reception that supposedly cost $500 a plate. ALL men were required to wear tuxes including any children.
If it’s s rule that people don’t really know then it’s not really a rule.
I think that most “rules” WRT wedding attire have been relaxed considerably in recent decades. Certainly wearing black to a wedding is no longer a faux pas. I do think the “no white dresses on wedding guests” rule still holds. And obviously it would be very odd for a wedding guest to wear a wedding dress as per the OP. Otherwise it seems that just about anything goes.
But I’m certainly no expert. These are just my observations as a guest at weddings over the years. I find most traditions surrounding weddings (and not just clothing-related traditions) outdated and sexist. Giving away the bride? Shudder.
And that is the main reason we didn’t have a wedding, just a civil ceremony in a courthouse. I wore a linen dress, the groom wore an open-necked shirt, blazer, and nice slacks (and he looked very sharp indeed). A very young man and woman were supposed to get married right before us. They were dressed in T-shirts, cut-off shorts, and flip-flops. The bailiff told them the judge wouldn’t let them get married in those clothes. The couple just shrugged and said, “Oh, O.K.,” and left. They didn’t seem terribly upset. I have always wondered whether they ever rescheduled their ceremony.
We were in the Navy and we eloped over lunch one day. I was in my khaki working uniform and my husband was in jeans - he was assigned to the base marina and they let him dress in civvies. Strangers signed as our witnesses - I have no idea what they were wearing, nor did I care. We just wanted the formalities out of the way so we could get on with life. It worked pretty well. 
Asked and answered already: Shodan’s mother.
It doesn’t matter what I think. Someone asked why the rule existed, and I answered. That just means I read Miss Manners’ books; it doesn’t mean I’m actually prepared to defend any of it. Albeit, without nice little rules like this, how else does one get to quietly and undisruptively register a protest? If people can’t have their polite little rebellions, they end up making scenes, and no one wants that.
Also mine. She cares passionately. So do most other people in my family, though not enough to scratch people of future guest lists for infractions, like my mother does.
BTW, if a wedding is in the summer, the daytime, and outside, it is all right for a woman to wear something that is basically white, but it shouldn’t look like a wedding dress-- say a white, short-sleeved blouse without lace or frills, and a skirt that is white with a floral print. A vest or bodice shouldn’t be white, or at least not all white.
Also, FWIW, the idea that you shouldn’t look like you are in mourning at a funeral is much, much older than the white dress for the bride.
If you are actually in deep mourning, and are observing it by wearing black, you shouldn’t go to a wedding, because you don’t go to parties while you are in deep mourning. For Jews, this is just during the week of Shiva, but for some gentile cultures, it’s a full year.
Which, of course, is why both Kate and William wore black to a friend’s wedding, and why black was the colour of most morning coats at their own royal wedding.
Sorry folks, but backwoods Mrs. Grundy’s have no business decreeing what other people should or should not wear at other people’s weddings.
British royals are another culture. Other cultures have no bearing on what is appropriate in the US. They wear white for morning in India. I have no idea how people dress for mourning in the UK, but what I know applies only in the US. Some of it my be regional, or Jewish, but let me suggest that if you ever do get invited to an Ashkenazic Jewish wedding in the Eastern US, you not dress in all black. You may send a message that you don’t intend to send.
OK, looked at the Royals’ picture. They do not look like they are in mourning clothes. The future Duchess of Cambridge would need a black dress with her jacket, and the prince would need black pants and a black vest.
I never said it is considered poor form to wear a single article of black to a wedding. I simply said you should not look like you are in mourning. I have a jacket that is black and white, and also black shoes, as well as a dress that was primarily green, but had a print, and black was one of the colors in the print, all to different weddings.
I have no control over what anyone else does, but people should be aware that there are quite a few other people who would be offended by someone showing up to a celebratory, milestone event, particularly a wedding, where some people do whisper disapproval, in all black. If you want to avoid the appearance of protesting the event, I would not wear black.
If you think you can strike some kind of blow for autonomy by wearing black to a wedding, then you’d better have a sign made, so people know you are protesting social mores, and not the actual wedding, because you really don’t want to be misunderstood.
Americans? Americans as in Ariana Rockefeller’s wedding in which the groom and groomsmen all wore black jackets and pants? They should have known better, I guess. And you’d best advise the fashion editor of the New York Times, while you’re at, it for promoting such faux pas.
Dressing for mourning is not a part of popular culture any more. I don’t think most people would have a clue as to what that was all about.
On the other hand, black clothing is a basic component of our every day business and casual lives.
Men go to work in black suites and ties. Charcoal and navy are also common but black s
Is basic. Women wear black dresses to gala receptions. Musicians wear black denims on stage.
Black outfits are not s sign of mourning in our culture to the extent that is really anything called dressing for mourning at all.
Dressing for a funeral iso more an exercise of applying a negative rather than a positive—don’t look disrespectful. Don’t look like you’re about to yell “woo” and knock back shots.
Black works for that in that sense, but not because black is an affirmative indication of mourning to us.
Again, cultural mores differ. Here, for instance, since burial usually takes place as quickly as possible - usually on the same day as the death - at least half of the people at a funeral show up in their work clothes. As a result, the only mourning symbols we have are the immediate family’s torn shirts.
Although, if you show up to a wedding with a gash in your shirt collar, then I guess you’re making *some *sort of statement.
We try to do burials here as quick as possible, but because of a lot of US red tape, the burial usually isn’t until the day after the funeral. That’s even more true outside New York and a couple of other major cities, where getting a kosher coffin might take a day. I’ve been to only a couple of same-day funerals, and those were both in New York, and for people whose deaths were entirely expected.
Again, RE: the black at weddings. I’m not defending it any position, just reporting what a lot of people I know think. Kinda like how I would never walk into an Orthodox synagogue in pants, with my head uncovered. I am not prepared to defend their ideas of modesty; I just respect them when I am among them, and I can tell you what they are if you ask.