I accused a girl of being too poor to afford a longer skirt and that she had to walk around in half of a skirt... she had a mini on, but she went with it and role played, until I got self conscious and ejected - ah the memories.
I like the neg opener because it establishes whether she can take a joke or not very quickly - just have to be careful how hard that neg is... some girls dont take negs well at all, sometimes it's that they dont have a sense of humour or they've just had a loss in the family or whatever... but it's still fun using a neg opener.