Here's a different story that feels low key to me...
One summer during uni, my gf (now mrs) and another girl shared a tiny two-bedroom flat. When I say tiny, it made us laugh as it was totally clear that it was once a one bedroom flat and that the landlord had simply put a partition wall in the middle of that bedroom. Thus it was now a "two bedroom" flat, albeit both rooms could only fit a single bed and hadn't room for much else. Still, the things you can put up with when you're a college student and have a hot girlfriend...
As a couple we were paranoid about the wall and the fact that it didn't provide much sound-proofing. That whole summer we never shagged at night-time, if our flat mate was in her bed. We still managed plenty, either during the day time or if she was gone out for the evening.
One such night, she headed out with some friends and we made the most of having the flat to ourselves. ;-) Later on, sometime after 3am I was woken by the noise of her coming back in. However, she clearly was not alone! She'd scored! I lay there awake, but pretty much unable to move as I was stuck between my gf and the wall on our single bed and wondered where this was going. Sure enough, she ended up inviting this chap into her bedroom and, presumably because of being drunk, didn't seem to care about the lack of soundproofing!
Between moans from her and the squeaking bed, it's clear they were shagging. I lay there listening to them, wondering if I should wake my gf... You'd think I'd have woken her straight away but 1. she always bangs on about loving her sleep and finding it hard to get back to sleep if she's woken during the night and 2. we had shagged just a couple of hours before. So I didn't.
However, just as the couple 'next door' were clearly reaching the moment of finishing (which took all of about 5 minutes btw) the next thing I felt was my lady having a full-on shuddering orgasm! Turned out she'd been awake for the last few minutes also, listening to them and (again) not wanting to wake me! She hadn't even rubbed herself though, I would have noticed, it was simply the horniness of hearing her friend shagging that send her over the edge.
Anyway, I'm going to put this in the low key thread as, even though we both now knew we were awake, for the various reasons mentioned above, we both decided not to do anything further and to try to get back to sleep. Still, we always had it as a sexy story to refer back to afterwards!