This is an opener I tried a couple of times and it works out really well.

"Hey, did you guys see that girl punch her boyfriend in the face? He de-pants her infront of a bunch of people and she just lost it. She didn't even bother to pull her pants up. She was throwing haymakers, half-naked. It was the greatest thing I have ever seen."

People always laugh and have a lot to say about it. The girls usually ask, "What kind of pants was she wearing that were so easy to yank down?"

To which I reply, "I think it was those weird gaucho pants, that girls are always wearing. That's what you get for wearing pajama's to a bar/club."

Easy way to start a conversation.

I have something similar that I use that I actually had happen to my group. "Did you guys see the half naked drunk girl outside? Get this...my buddy was talking to this girl outside having a smoke and out of no where she decides to take her jeans off because she's hot. She's standing there in her panties and the bouncers won't come near her because I guess they're afraid to get sued, and prob because they were having a look."

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Been around the world twice, Talked to everyone once...

I like openers that involve something that is going on at the venue. It feels more natural and less manufactured.