So someone asked me this the other night while I was at work. I started asking girls this question as an opener, and nearly every girl out of the 10-15 I asked responded with interest and enthusiasm. Mind you, I was working, so I couldn't really hang around and keep talking to them much longer than it took to hear their answers. Also, it should be noted that I work in a bar, so this probably shouldn't be used in day game. It goes like this:

If you had to choose between either replacing one of your hands with a second vagina, or replace your vagina with a third hand, which would you prefer?

From there, I did a little bit of joking, and used this as a little bit of a cold reading technique (if opting for the third hand, they might not value sex as highly, etc...)

Led to a lot of hilarious conversations. I originally heard it as directed towards guys (so replace "vagina" with "penis"), and it worked to build rapport with other guys in groups, as well.