Abuse of any kind
Close-mindedness
Pessimism (when constant)
Criminal record (I've dated a handful of guys that have criminal records because I always feel that people deserve second chances... needless to say, every single one of them ended up back in jail while we were together or shortly after we broke up. Not doin' it again!)
Inability to think for themselves (I dated a guy once whose mother had made every decision for him growing up, bought his school clothes without even taking him shopping with her, etcetera. As an adult, he was a horrible decision-maker. Parents: Let your kid make decisions and make mistakes!)
Illegal drug user/heavy drinker (I would give a pass to marijuana as long as he wasn't a total pothead that smoked every day or whatever. Occasional/social drinking is okay too, just not every day, and not if they get shit-faced drunk a lot either.)
Lying (I've been lied too so much growing up that I have zero tolerance for it anymore.)
Not doing what you say you are going to do (To me this is just a respect thing. If you say you are going to call, then call. If you say you're gonna come over, come over. If you say you are going to take out the trash, then take out the trash. Not sure if this again has to do with all the drama of my childhood, but I really really can't stand it when someone says they are going to do something and then they don't. If something comes up and you can't come over, that's fine, just let me know. Don't just stand me up.)
Porn addiction (Eh. Weird one, I know. I get that guys aren't as imaginative as chicks, more of then they want to use porn to jack off, but if you are jacking off to porn every day and WE aren't having sex, and you can't seem to stop doing it, then we're having a problem.)
Poor hygiene (I dated a guy once that smelled really bad. I did some searching online and checked his shower and realized that while he bathed every day, he wasn't using anti-bacterial soap/body wash. I brought it up to him gently and he admitted that lots of people have told him that he stinks. I explained about the bacteria and we went out and got him some anti-bacterial bar soap to wash his pits/junk/other sweaty areas with and voila!- no more stink.)
I think that's about it. All of my deal-breaker list, for the most part, is based on issues I had in previous relationships.