This one kinda requires a specific situation and seems stupid, but it works pretty well for me:
If there's a guy dressed kinda douchy who is on the dance floor trying to look like he's all that, I approach a girl/a small group of girls (no more than 3) and say "I bet you a round of drinks you can't beat that guy in a dance off". If the guy is outrageous enough they'll laugh and be pretty into the idea. Sometimes they'll be afraid to look stupid, in which case I tell them I'll join. Afterwards, jokingly argue about who is the "winner", and just say "How about we just call it a draw and we both buy each other a round of drinks?". Seems lame but they always are really entertained by it and will practically beg for your attention. Even if they refuse to do the dance off it'll still be a good opening laugh.