How do you know when a guy just wants to have sex?

A guy who wants a relationship with you (a real relationship, that is) does not begin a conversation with, "So, what makes you wet?" By the way, if he is asking you this question, and you don't know him that well --- do not fool yourself into thinking YOU are the only girl he asks. He is creepy to speak to you in this manner. HE JUST WANTS TO HAVE SEX.