If I were to suddenly find myself in the dating pool again, I would say the following are dealbreakers:
-Smokes (I do not enjoy the cool taste of menthol when I make out with someone)
-Doesn’t drink (I should be able to enjoy drinking wine, margharitas, martinis, mohitos, scotch, etc with you)
-Bad drunk (that does not mean I want to clean up after your mess)
-Fat or ugly (sorry, I’m shallow)
-Crazy drama (I am not auditioning for a reality show. Do not create problems.)
-Sexually repressed (you do not need to be down with the funky shit, but you should not treat your vagina like it’s King Solomon’s lost mine unless you have a box of Alan Quartermain condoms to go with it)
-Tedious (I shouldn’t feel like I want to rip my own arm off just so I have something to stuff in your mouth to quiet it.)
The drinking deal-breaker could be a factor of age. I was a whole lot more into parties and drinking in my twenties than I am now in my forties. I’ve seen my husband drunk about three times in 10 years, and once was after his stag, where his good friends made it their mission in life to wreck him. He’s never seen me drunk since I don’t drink to excess (no higher morality there - I just get hangovers from two beers). At this stage in my life I wouldn’t date someone who wanted to party it up every weekend - leave that for the kids who can still handle it.
No one said anything about every weekend, but if you can’t declare triumphantly, “You know what? It’s [insert occasion here… hell, screw the occasion, it’s not required], and I’m gonna tie one on!” ever, then I don’t wanna go out with you.
My breakers:
-hyper religious
-obsessed with money
-dumpy and unkempts
-heavy smoker/drinker
-indoor type
In my dating days, some of my dealbreakers were smoking, neediness/clingy-ness/insecurity, no sense of humor, bigotry- these, not surprisingly, have been frequently mentioned. A couple that haven’t, though (unless I missed them):
Vegetarian/vegan. I don’t judge these people harshly or anything, it’s just that I knew I’d eventually resent the limitations the lifestyle would cause. (And yes, I fully realize it’s healthier.)
Taking astrology seriously. These people, on the other hand…
If it smells like an outdoor pet, we have a whole nother set of problems.
True that is a bit of an omission. Granted I have a co-worker for whom it’s such a non-issue (amicable divorce) it didn’t even occur to him to mention it to his current girlfriend for a couple months. For my co-worker and his now-ex-wife, with everything being friendly it was abut as dramatic as getting the paperwork done to get a passport.
But yeah, I would consider a divorce in progress to be “potential drama I would like to know about” early on, so I guess that’s understandable.
Ugh! How many times do people on this board have to re-iterate that “bisexual” does NOT mean “non-monogamous”. If non-monogamy is a deal-breaker, fine. But non-monogamy is not a required feature of bisexuality, hetero spouses can be shared too.
That’s certainly debatable.
I agree. I was going to elaborate more, but it’s more of a whole 'nuther thread thing.
It wouldn’t be a deal-breaker for me. In fact, if the person is fiscally responsible and plays well with others, that’s a plus.
I’m a single guy. Some deal breakers for women:
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Religion: too religious (wants to save or convert you; is a strong adherent to a belief system that prohibits things like drinking, dancing, premarital sex, and the like; or thinks you’re going to Hell for not sharing her beliefs), too atheist (SDMB-style militant atheism; e.g. “Look at those brain-dead sheep going off to sing to their sky wizard!”), or an oddball/cultish faith (Scientology, JW, rural Pentecostalism, Primitive/Hardshell Baptist, maybe Wicca/neopagan beliefs).
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Extremely strong ethnic identity to the point where culture clashes are inevitable, her family and friends won’t accept me, I’m pressured to adjust to her values and mores while she feels no obligation to adjust to mine, and so on.
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Extreme politics to the left or right.
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Kountry kitschy/glurgey; e.g. a middle-aged administrative assistant who has a cubicle filled with Cathy strips and cat photos, who forwards inspirational email to everyone they know.
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Not intellectually curio.
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Working-class with no post-secondary education.
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Too serious; seldom or never laughs.
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Racism.
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Offends too easily or too PC: e.g. wouldn’t see a Cleveland Indians game because she finds the team’s name is offensive, finds SNL ESPN Classic skits offensive (“When you got something fungal deep down in your lady jungle”), etc.
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Mental illnesses that would affect my well-being: e.g. bipolar, schizophrenic, borderline personality disorder, history of cutting or disfigurement, etc.
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Physically disabled or disfigured. This includes facial birthmarks and burn victims, and diseases that will require me to be more of a caretaker rather than a partner. Sorry.
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Too many tats. There’s a difference between a shoulder or ankle tattoo and “My body is a canvas!”. Likewise, chest and breast tattoos.
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Has a greater physical presence than me; e.g. wider or taller.
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Hirsutism; moustaches, really hairy arms, unshaved legs/pits, etc.
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Ugly. Not “her knees are too sharp” ugly, but rather with truly unpleasant facial features or odd proportions.
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Seinfeldian realm: “man hands” that are bigger than mine, odd fingernails.
I know, but still, in the experiences of my friends, and what I’ve seen in online dating profiles, there’s a VERY strong corollary between bisexuality and polyamory.
A couple more, just to be pickr:
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Prudery, like others mentioned.
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More than two kids, or they have two daughters. With two girls, if the relationship becomes permanent, odds are it’ll become an “us versus them” scenario. Likewise, kids of an age where I get none of the benefits (bonding as a father) but all of the responsibilities (financial support).
Sometimes it’s not our fault, though. 
I would love to go out and get smashed. Unfortunately, I did enough of that when I was in college and coupled with a decade or so of intense internalized stress resulting in a borderline ulcer, it is now impossible for me to get to a “fun” drunk stage without immediately ending up in the bathroom 20 minutes later wanting to die.
It f’n SUCKS. I can get a good buzz on for about 15 to 20 minutes, then the nausea sets in. If I keep drinking after that, I am in for a world of hurt. Hence: no boozin’ for me. I’ll still drink socially, but certainly never more than two drinks or so. It’s just not worth the near death bathroom experience I will inevitably face later on. It’s unfortunate, because I certainly like to drink, I just can’t, really.
I’ll totally kick back and smoke a buncha pot with you though. 
If you ever find yourself in central PA, I need a new drinking buddy. Discovery of same being a perfectly valid occasion to tie one on.
In which case is the undesirable issue bisexuality or polyamory? If you’re dealbreaker is non-monogamy then just say “non-monogamy” rather than make assumptions.
Instant deal-breaker? Smoking. No doubt about it.
Other deal-breakers have been covered already, but they include[ul][]use of hard drugs, []disrespect for others including exes (she badmouths them all the time, I know she’ll badmouth me eventually too… and there must have been something good about them as well, or she would have never hooked up with them in the first place), [] constant swearing (come on… you can be more original than that),[] lack of reading,[] lack of intellectual curiosity, []proselytization (if you think your religion is more important than the people around you, you can have it instead). [/ul] Note that ‘fat’ is not on this list; my last two girlfriends were fat and I didn’t mind at all. 
I’ll celebrate my 20th wedding anniversary this summer, but if I were dating again, in no particular order:
smoking
drug abuse
serious obesity
pushy religious witnessing
severe body odor
frequent and pointless profanity
Awwww, that’s so sweet! Can you post pictures of the kitties?
Anyone else having cognitive dissonance between the username and this post?
But it’s one helluva cat.
Hmm. Smoking would be a powerful disincentive, but not an instant dealbreaker.
Excessive religiosity would be one, though.
Lack of a sense of humor would be one.
The couple of times I’ve had to shut something down before it could potentially evolve into a relationship, one of two things was to blame :
Clinginess - I can’t pay attention to someone every minute of every day. I need time NOT doing that to retain my sanity. Independent women = good.
Craaaaaazy - This one’s hard to quantify, but from some folks, you know how you can get that vibe that while they’ve maybe never been an axe murderer, you’re still a little worried what might happen if you got them near an axe?