like you said earlier, some guys are just jerks. it’s not so much assuming that had they already fucked you, they wouldn’t be talking to you anymore. but trying to see where on the priority scale fucking you lies (no pun intended). imho std (sex on third date?) is better that sfd. it’s easy to keep up the charade and still present yourself as the knight in shining armor, especially if it’s only the 3rd date, but at least this way you can learn a little bit more about the other person. by the 3rd date you would have had enough mindless chit chat to know:

1) i have chocolate and vanilla ice cream, which do they prefer/should i bring back into the bedroom?
2) perhaps touched upon the topic of food allergies – what should you not try to make them for breakfast in the morning (b/c if in fact you really are interested in a relationship and not just sex, chances are you’ll be trying to woo them the next morning with something cutesy and vomit inducing–like breakfast in bed)
3) i’m not sure i remember what i wanted to put for #3, but i’m guessing it also had something to do with food.