A friend and I rented a small one-bedroom apartment off-campus in my senior year in college. We had one bed, and I'm sure to visitors it looked odd, but we didn't sleep together or have sex of any kind together. He slept in the bed, I slept on the floor in the bedroom. Sleeping on the floor seemed good for my back anyway, or at least I thought so.
But in such tight quarters, I had to find a way for relief. Jerking off when my room-mate was away was one thing, but at night, what about that? I often slept completely nude, so by the time I hit the hay, I was ready for business without having to move around to get my clothes off. Usually, after it seemed like all was quiet and my room-mate was probably asleep, I would take my frenum, that little bit of skin below my cock head, between my thumb and forefinger and roll it back and forth quietly. I am circumcised, but have enough skin left for this to be a really pleasurable way to get off. Eventually I would be wet with precum, giving me another way to push to orgasm: sliding my thumb over the head of my wet dick, which was by now very sensitive. Then I'd go back rolling my skin again, until finally I'd come in waves and waves.
Did my room-mate ever know about this? Maybe, but he never let on. I assume he had some similar technique that I never noticed. One thing I do know, though: Masturbating and coming to orgasm while we were both in the same room was a thrill.