The other day as he was leaving the room, a boy in grade 7 commented, "You make learning about sex fun!" which I took as a great compliment.
I had a girl ask me, in all seriousness, "Can you get pregnant by swimming in a pool?" I assured her that although sperm are good swimmers, they're not that good. They don't have radar that helps them find vaginas.
While discussing reproduction, a student asked me how the X-men got their powers.
When I talk about condoms, I mention that although they reduce risk of pregnancy and STIs, they're not perfect. Especially because some STIs are transferred by skin to skin contact, and condoms aren't a fully body wet suit. After saying this one time, I had a high school boy say, "Well, what if I wrapped myself up in seran wrap?" I looked at him and said, "Do you really think some girl is gonna wanna get with you when you're covered in seran wrap?" and he thought about it for a second and said, "You're right. How about tin foil?"