Well other than shitty drawings in school, and Geri Haliwell or Pamela Andersons muffs appearing in the Daily Star, the first real graphic upclose picture of one I didn't see until around age 9, the image is still burned into the back of my eyes.
It was a woman lying on a bed arching her back, spreading her legs and holding open her pussy. I didn't know what the fuck was going on.
Then that same day I saw two women lying sideways back-to-back sharing a double ended dildo. I thought it was a tube passing fluid in and out of them both. Once again, I didn't know what the fuck was going on.
That is quite something to lay on a kid who hadn't even done sex education yet.