These aren't quite proper 'danger wank' stories, as I wasn't in actual danger of someone walking in and seeing me wanking- more like wanking in indiscreet places with people around who might easily have guessed what I was doing. I hope it's still ok to post them.
1) One was from when I was acting in a play at university. For the dress rehearsal, we had only been given one room for 'backstage' to get changed in. Most of the female students in the play went and changed in the toilets, so the men wouldn't see them- but one girl (a 'theatre-girl' type) tried to show how professional she was by getting changed there with the guys. She was quite busty too, so I got a great view of her big boobs in a lacy white bra, and her lacy black knickers as she changed.
I have a thing for women's underwear, so this was a major turn-on for me. Without thinking too clearly, I walked into the men's toilets nearby, went into a cubicle, and had a quick wank- I came into a tissue I had in my pocket. The door of the cubicle was locked, but anyone could have come in and might have heard what I was doing. I bumped into another guy as I was coming out of the toilet, hoping I didn't look too flustered!
2) When I was about 20 I went to a house party at a friend's house, while his parents were away.. We were up drinking til late, and lots of people had brought sleeping bags to sleep on the floor. His house was quite small so that meant that a couple of girls were sleeping on the living room floor with most of the guys.
One of these girls, L, took her jeans off inside her sleeping bag, so the boys wouldn't see- but then remembered she'd left her phone in the kitchen. L said "Oh fuck it!" and got up to fetch it, showing us all her gauzy black knickers which were kind of see through at the back, so her ass showed vaguely. A couple of the guys laughed.
Next morning I woke up before anyone else, with a morning wood erection. I could see L's sleeping head lying on the floor in her sleeping bag, close by. The temptation got me, and I reached down and started to stroke, looking at L's face and imagining the flimsy back panties on her ass. I began to get closer, and caution got the better of me- I tucked my erection into the waistband of my boxers, and went upstairs to the toilet, where I finished wanking and came into a wad of toilet paper.
2) This story is kind of a reverse danger-wank; when I actually heard another guy wanking when he thought I couldn't hear.
I was staying over at my friend's house- we were 19 and lived with parents, so I was in a sleeping bag on his bedroom floor. In the morning I had woken up, but was lying with my eyes closed trying to go back to sleep. I heard him moving slightly, and then heard a rhythmic movement of the covers rustling. There was no doubt, he was having a wank, thinking I was still asleep.
I didn't want to risk him knowing I might have heard, so I pretended to still be asleep- and a couple of minutes later, the noise stopped and I heard a soft sigh- he had cum. I then heard him going to the bathroom, and decided it was safe to 'wake up'.
I'm not into men, but nevertheless it wasn't an unpleasant experience, hearing him wank. I just thought it was rather funny.
