--> Boys who are skinnier than me. I'm relatively fit, so if they're skinnier than me, it looks unhealthy to me.
--> Short guys. Which is unfortunate, because I'm 5'9", so I'm kinda tall for a girl, plus I like heels. But that's kind of the point: I want to be able to get dressed and go out with the guy without feeling like Godzilla.
--> Guys who dress poorly. Dressing well doesn't have to be designer clothes. But guys who really take no time into getting dressed before leaving their home (the low slung jeans with the underwear hanging out, the oversized sweatpants, the sweatpants-sweatshirt combo on a whole) means that I don't have to take time into getting to know them either.
--> Body odor. Just yuck.
I could mention some other things, but those are the real deal-breakers for me.
Oddly enough, smoking doesn't bother me. I think smoking is only really unattractive on girls (something about a pretty girl, with a cigarette in her mouth, and spitting every few minutes from the smoking, is not cute). Luckily for me, I like boys. I don't smoke myself, and I'm not a supporter of smoking either, but that's that person's choice. So long as it doesn't interfere with my relationship with you, I'm fine. One time I was dating a guy, and we were mid-cuddle, enjoying each other's company, when he suddenly needed to run outside for a cigarette. This counts as interference, and we soon stopped seeing each other afterwards.