ways of secretly rubbing "up" on a guy

[D_45rtgh]

I was wondering what are some ways of secretly rubbing up on someone like in a club or something. without offending someone.

 

[MrHangman]

This is weird. I think it's called frottage and it's illegal. But I'll tell you when I go to concerts, sometimes I feel like the guy in front of me is rubbing up into me too much. But then again, he probably thinks I'm rubbing onto him too much.