Back before I started whittling my bedpost down with notches, I was at one point a virgin.
My first penile encounter was in high school, with a good friend's brother. He was a freshman, I was a senior. Technically statutory. If you want to get technical. Mostly I liked him because he had given me a copy of The Presidents of the United States of America CD when I lost mine, and we watched Iron Chef (the Japanese version) together. We didn't have sex. Held hands, kissed, touched each other's genitals. High school stuff like that. Mostly I remember things being very quick and fairly unexciting.
The first time somebody else gave me an orgasm was also in high school. It was at a party that was winding down (I don't remember if there was underage drinking or not, it's entirely possible). It was a weird grouping of people - mostly friends from drama and band, but a few friends of friends as well. Myself and one of the friends of friends were making out on a couch when he slipped his hand into my pants. I'd given myself orgasms before this point, but this was completely new and extraordinary.
I first made another woman orgasm my sophomore year of college. She was a friend I knew from the LGBT group in my dorm complex. I remember especially loving her nipples, the noises she made, and actually being able to feel her vaginal walls contract around my fingers when she came. This was a moment realized for me, that not only did I think women were sexually attractive, but they were also amazingly fun to have sex with. To this day, I get a ridiculous goofy grin when giving other women orgasms.
These three are particularly acute memories for me when I think about checking off the sexual experience list. There have been many other firsts since then (first anal, first threesome, first time in bondage, first pegging, etc.).