fact: i actually once caught a friend of mine jerking off. we were sharing a room (separate beds) on holiday. i woke in the middle of the night because of a hayfever attack. i couldn't breathe and i thought i was hallucinating when i heard frantic movement from the bed besides mine - then i heard the following sounds in this sequence:
- an elastic slapping something
- a packet of something being opened
- nondescript other noise
- again, an elastic slapping something
- my friend turning in the bed
- his breathing turning to slow and steady
(his hand came out of his boxer shorts, went straight to the nightstand to get and open the tissue packet; he cleaned himself up with a tissue, then his hand came out of his shorts again, and he slept, finally satisfied)
the following day i gave him hell for that. i still occasionally give him hell for that, come to think of it.