"I can fix him!" Seriously, the biggest red flag is a woman thinking you are a broken bad-boy who needs to be saved/put back together. They are the type that will deconstruct your life, and try to rebuild it their way. Nobody wins something like that. You'll hate it, and she'll come to hate you for hating it. Note that this is different from a woman just being attracted to bad-boys/dangerous men. That's pretty normal, so long as they aren't lusting over serial murders or the like.
The second big Red Flag? I hate to say it boys, but casual sex. I have seen two instances of fuck-buddies falling into stable relationships with each other. All the rest? Hoes don't make housewives. I'm sure there are a billion extremely good but autisticly...