One of the people in my choir class wanted to try on me. Even though the thought of sex has always made me uncomfortable I figured it couldn't be too bad to just let her try (it was just with my hand, after all). Giggling, she yanked on my fingers, and I frowned and said, "ow!" I didn't know about asexuality at the time, but heck, if I did that probably would've clued me in big time.