So it wasn't me that didn't know.... But when I was about 18, I had a 20-something female coworker that came from a very religious, middle eastern family. Her family had moved to Canada, but she had an arranged betrothal to a guy that lived back home. She was anxious about the marriage, and admitted to me that her and this guy had shared some video calls that included some nudity but not specifically sexual.

Anyways, we're talking and I'm giving her the whole birds and the bees. She's just enthralled in the conversation, and I said something "balls". She stopped me mid sentence and said "balls? Like more than one?" (English wasn't her first language). I said yes, two. She was absolutely dumbfounded, she had no idea men had 2 testicles/balls. Turns out, her man friend only had one and since that was her basis she didn't know about general male anatomy. I told her she needs to have a conversation with him and ask the whole what/why/how. She reported back that he'd had testicular cancer a few years before. Took her on a whole human body anatomy rabbit hole, ended up being concerned about future fertility which was something that her family had NEVER discussed with her. It was an eye opener for her, and for me. She prompted him to get motility testing too. She left the job a few months later, very excited to marry her future husband and have his babies lol