I remember a book in which the anthropologist Desmond Morris asserted that men and women, by and large, turn in different directions when brushing past people in a close space: men tend to turn toward them, women away.
Edited to add: By the way, wouldn't that be "bumming" rather than "butting" in the UK?
It was a scene in Fight Club...
Brady Pit walks up to Ed Norton sitting in the isle seat of the plane. Pit asks "But or Nuts"
Norton says "What?"
Pit then just slides into the window seat with his butt facing Norton.
Pit talks a while and then gets up to sit by a pretty young lady also sitting in the isle seat (again giving him the butt). He just turns towards her and gives her the nuts and smiles at Norton down the isle.
It is very subtle but funny.