Alot of these go without saying... I mean, nobody says "Hey, look at that dirty obese girl over there... Think she'll date me?"
Physical:
Gapped teeth (a.k.a. Chiclets)
Stretch marks
Braces (well good gawd, I'm 25, lets hope so!)
Short hair
Frumpy clothing
Facial hair or excessive peach-fuzz
* there's more, but these are the big ones *
Mental/Emotional:
"I'm fat!" (but isn't really)
Gossip queen
Drama queen
Snob queen
Paranoid delusions
* Again, these are just the relationship breakers *
This isn't to say that I couldn't be friends with some of these people, but intimate relationships are pretty much out.