Hmmm...
When I was a little girl, I had a friend who would want to watch me every time I peed when I'd be at her house to play - she'd make me spread my legs, and she even touched the stream a time or two. I was pretty submissive as a child, so I didn't really think anything of it.
The first purely bdsm sexual experience was with my first lover. She would make me sit on her face, and she'd claw and heave, but she'd beg me not to get up until she slapped my ass...but that's relatively tame, I guess. It got more intense, and strangely, less pleasant for me as time passed.