What if it’s someone you’re already in a relationship with?
I can see not wanting to go on a first or second date with a cold sore, but if you’re already involved (but not married), is breaking the date necessary?
I dunno- I like to make out with my dates. So, I’d hope you’d reschedule, rather than infect me. 
[ul]
[li]Any use of tobacco, in any form.[/li][li]Any possession/use of any illegal drug.[/li][li]Mistreatment of any animal, except for velociraptors.[/li][/ul]
Dirty ears.
Ever look at someone’s ear and see crud in the opening? If you can’t keep your ears clean, then what about the rest of you? Bleh!
Oh, or spittle formed on the corner of the mouth. That makes me want to vomit just typing it.
Confusing “your” and “you’re” would be a deal-breaker.
Tattoos. There are maybe a handful of girls in the world otherwise hot enough that I could overlook how much tattoos gross me out. And they’d be far too hot to ever date me, soooo…
So you only date ventriloquists? 
I find it really cool when people set high (but bizarre) standards for themselves and stick to it.
Not washing one’s hands after using the toilet. Obviously it would be hard to determine unless you were at an intimate enough setting so as to be near the bathroom.
I had a boyfriend that didn’t wash his hands after using the bathroom, but I didn’t know that about him until after we’d moved in together. There were other issues between us but that was the filthy icing on the unhygenic cake.
Lesbian here, and I’d say long hair. Long hair on women is a complete turn-off for me.
Any of the above mentioned hygiene challenges. I will never again try to overlook a hygiene problem. They do not cease to disgust me, and my experience is that this never changes.
Hair too done. If a guy looks like he spent more than about 5 minutes on his hair, I’m outta there.
A friend told me a story about a guy who, after the meal was finished, reached down and pulled a thread out of his sock, then proceeded to floss his teeth with it.
I can deal with the nosehairs, I suppose, although I’d like to think you can tame them a little. Bad hygiene, though, no way. I once gave up on the idea of even dating this sexy Russian man I knew because his breath stank like someone had crawled into his mouth and died.
Breaking wind? You can handle it for a few hours, and if not, then you probably shouldn’t be out on a date. I wasn’t aware “most of humanity” has a problem with breaking wind noisiliy and pungently several times in an hour.
And I won’t date anyone with visible cold sores on their lip, either. yes, yes, I know, now for the speech where EVERYONE HAS HERPES and I should just get over myself. Maybe everyone does, but I have never ever had any symptoms so why take a chance? Maybe I don’t have it.
And of course the other one is spitting in public. Instant, sudden dealbreaker. I may manage to finish out the date, if he only does it once. It is a disgusting habit.
Anything hygiene-related that could have been taken care of in 20 minutes before the date - I don’t think it’s a lot to expect you take a shower, wear deodorant and brush your teeth.
Also, facial hair and long hair (on men) are deal-breakers for me. I understand some women dig it, but I just don’t find that attractive at all.
I’m glad you added the second part there; I was worried for a second.
I’ve been out of the dating scene for a bit of time now (10+ years) but I know a girl who always absent-mindedly pops her knuckles. She does every single one but not all at once; each one individually. She could be watching a movie, eating, talking whatever and it starts: Pop. Pop. Pop. Each one jarred my soul.
I married her anyway though; I’ve been training her out of it.
Especially since there is a huge pool of men that *are * willing to do it.
I thought about this, and realized it depends on how much hair. A light mustache or a shadow, maybe. A giant beard? Never.
If she has a penis … I’m done.
I guess it depends on where one draws the line at “problem.” Everybody farts. 
Oh! Spitting in public doesn’t bother me much. I knew my boyfriend before we were dating and he does this - not all the time, usually into the gutter or out the car window. I suppose it’s kind of gross and rude but I hardly notice it. Also, I don’t care about belching.
MeanOldLady, I don’t think my standards for body function control, hygiene and looks are unreasonable, but then I see some of the guys my friends date! Apparently many, many people are less picky than I.
Any man who wants to have a chance at touching me has to at bare minimum smell good and look clean and neat, be ‘in good shape’ (no beer belly, some muscle tone), have decent skin (I don’t mind a zit or two), no open sores or uncared for wounds, straight and healthy-looking teeth, unobjectionable breath, smooth and clean lips, short fingernails (long nails on guys make me want to die for some reason). All that is just enough to keep me from feeling physical disgust at the thought of having sex with you.
Hey Duckie, hold my blunt while I stomp this kitten!