"When you have sex, and you're on top, do you wear your hair open or as a ponytail?" Okay, kind of crude, but I had a girl ask me actually, I had long hair back then
I've been to speed dating once, and from what I could tell most girls there weren't sluts at all, but just normal girls curious about that thing. Curious, and very wary of you trying to pick them up! They're more interested in having 20 guys try to impress them in a row so they feel good
I don't think you can "pick up" a girl in 3mins (if she's not a slut hehe). So don't try to "be fun", but rather have fun. Don't ask the same questions after the 3rd time, because everyone does.
ANYWAY, ask some witty stuff, and if you can't think of witty, think something crazy, anything really. Your real chance is AFTER the speed dating, if it's at some pub or cafe then people stay and you can start your game. +you have social validation from pretty much everyone in the room, so perfect conditions!