I'm bored, so I hope you won't mind me invading briefly.
I don't remember mine, but I probably had to be forced into it (I wanted to run around shirtless, dangit). It was probably a sports bra too. I wore those until 13, when I had precisely one bra and wore it until I replaced it with binding materials. Then threw it out.

I remember my first man's underwear though, and like you ladies stealing your mother's or sister's bra, I stole it from my dad. I would like to stress they were clean underwear...(doesn't make it any less weird though, does it?)