Mine's funny as hell ...
It was two weeks before high school graduation, two months before my 19th birthday, and we decided that since school was having a half day for seniors, we would go off-roading that afternoon.
Up to this point, we have been nothing but regular friends - shooting bullshit at each other, trying to set the other up on dates (I don't know how many of my female friends I hooked him up with), and only one kiss between us (a surprise b-day gift to him).
So here we were, middle of nowhere quarry, and we get stuck on a huge pile of sand. Two more feet, and we would have ended up with our noses sticking out of the back of our heads. We spend the next two hours trying to dig his truck out, getting incredibly exhausted and dehydrated, until he runs off to find some help. Lo and behold, the boy finds a front end loader to pull his truck out. It worked, left a note to apologize for letting it run out of gas (we may have been stupid, but we were polite ), then limped back to my house to clean up.
My parents were out of the house when we got there, so we took turns showering, then sat in my room in our towels and talked ... I came onto him ... he accepted and started to lead ... then we suddenly found ourselves completely naked and humping like stoats. He had a few other girls while I was a complete virgin, so he tried his best. Hurt like hell, and a few fantasies were crushed, but I still regard the experience very warmly.
The capper? Fourteen years later after shitty marriages to other people, we're back together again and I'm really enjoying it this time.