One Christmas, when I was like 14, I jerked off in a jacuzzi tub at my grandparents house, and like half an hour after I finished my female cousin went in and took a bath. For like 2 weeks I was sweating bullets thinking I'd for sure gotten her pregnant.
*Edit: The same year, I was bored at a relative's house and got the idea that I needed to try to weigh my boner on the bathroom scale (I reiterate: I was 14). I hoisted the scale up onto the bathroom counter, worked myself up to a chub, and right as I was about to plop my dick onto the scale my uncle walks in.
We've never spoken about it.