Two things that ruin dates quickly, I've found, are exposing girls to my Star Trek Commemorative Plates and my "How Many Twinkies Can I Fit In My Mouth at Once?" trick. I prefer to let girls discover my stash of commemorative plates naturally on their own volition, with them removing the black tarp in a scene eerily reminiscent of when the lady stumbled upon the Phantom of the Opera playing the pipe organ and removed his mask.
The answer, by the way, is four.