What's this about?

My guess is that the two on right have had a bit too much to drink and, without their thinking about it, one thing has led to another.......As for the guy looking on, though I don't think he feels particularly left out of it. I reckon he's not gay (or that's what he says!) but is curious as to how things are going to develop. Well, I think we can all tell him - but will he himself be a participant?