Well. Depends on who you ask, I suppose.
I've always found that to be kind of an axiomatic question. I mean, if we're already supposing there is a "worst," doesn't that suggest the potential for something pretty bad?
We never ask this question before eating ice cream, for example. Or going out to dinner. No, this question is reserved for those moments in which we know we are about to do something singularly dangerous, ill-advised or just plain stupid.
I think it's safe to say that there are two kinds of people who ask this question. Those who care about the answer, and those who don't.
Those who care about the answer tend to stop and ponder their next move. Those who don't care about the answer ask the question with great irony and bravado. They really just want everyone around them to know how cool they are. "Hey! Look at me!"
Or...maybe they just have nothing left to lose. Maybe the worst has already happened to them, and it just doesn't matter anymore.