Mentioning other guys -- "that (name) is so attractive" -- this kills any interest I might have in her. Instant friendzone for me, period.
Providing INTIMATE details about the relationship she used to have with her ex, even if you didn't ask. Huge turn off as well. Please, I don't want to hear that sh*t.
If I see her flirting with some other guy. Not just chatting or laughing, but clearly flirting: making eyes at him, acting coy or mischievous, touching him playfully, anything like that. Another instant friendzone there.
Tries to play games with me -- obvious attempts to make me jealous, or get me to fight for her attention; or playing hot n' cold; or any other stupid little game women like to play. For me it's a clear sign of immaturity, so the most she will ever be is a friend. Probably not even that, though.
She has issues. Of course, everyone has their own share of problems, but some are deal breakers and no-no's for dating: a strong resentment / spite towards men; still in love with her ex, or has a thing for some other guy; is very, very sexist and tries to enforce that in her relationships, making the guy pay for everything and take her anywhere anytime, because he must "provide" for her; and other things I forget atm.
Finally, if she lacks a fundamental quality that I consider... well, fundamental. Like being level-headed, trustworthy, sincere. And of course there must be some degree of attraction.
Hope this helps. Good Luck.