What do guys expect to happen when they dance behind you in clubs?

A guy who rarely talks to me but stares at me, we were at a club and I was singing karaoke and he came up behind me and put his hands on my waist and just stayed there. I felt awkward because I don't know him very well.

What do guys expect to happen when they do that and why do they do that instead of just talking to you?

What do guys expect to happen when they dance behind you in clubs?
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