How about this one?
You: "You know, we have been going out for a couple of months now, and I think you are really great..."
Her: "Aw, that is soooo sweet!"
You: "Yeah, anyway, I was hoping that we could take our relationship to the next level."
Her: (with knowing look in her eye) "I was thinking the same thing."
You: "Well, I think you need to get ckecked out. You look like a nice clean girl, but in my experience looks can be decieving. I really want to bang you, but if I am going to do this properly, I need a bill of health. Dad always said 'Careful of the ladies son, they'll screw you over' and I always took that to heart, sexually I mean. So how about you make an appointment and get the tests back to me in writing ASAP. You are hot, but so was that girl I did in Amsterdam in '94 and I'm still paying for that one...."
Her: (Silence, with look of horror)
You have any other ideas?
