Some personal bail points of mine:
Too many characters, not enough personality:
Especially common in the "youth crew" type stories, where there's a whole gang of gay/bi kids and couples. Twelve characters who all speak, act, and look the same can get pretty old, especially if they all start pairing off. I mean, you can only stand to watch so many identical teen couples getting together before you start to think "Hey, this exact same thing happened two chapters ago...why am I taking the time to read it again?"
Celebrities/Sci-Fi coming out of nowhere:
I've seen a few stories that started out great, completely original, but then all of a sudden, a few chapters in: "You mean that guy from Hanson is your long lost cousin!? And he'll fly us to the set of the new Harry Potter movie in the Millenium Falcon!? *gasp* Look out, SPACE NINJAS!" I've got nothing against Sci-Fi authors and fan-fictionists...it's just that I'd prefer some kind of warning ahead of time.
Of course, the ones that other people have mentioned apply to me, too: Too much sex, too much kinkiness, plot lines that don't go anywhere, hospital scenes, etc. However, I can usually look past those. The above two, on the other hand, are immediate bail points for me.