I guess I learned about it in sex ed (5th grade I think) and some stuff I learned from other kids, (like how pregnancy only happens when you do some mysterious act with the opposite sex) but it's not because my parents were unwilling to tell me, I guess they just didn't see the rush. I remember one time I asked my mom to explain a sex joke from a TV show and she told me about erections and arousal. She was a little embarrassed, but she explained it well enough.
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"You gotta keep making decisions, even if they're wrong decisions, you know. If you don't make decisions, you're stuffed."
- Joe Simpson