As kids, we usually think of our families as "normal" until we get old enough to have friends over. That's when we learn the ways in which our families, and their rules and traditions, compare to other people's.
Someone asked Reddit: "What was a rule in your house that you thought was normal until a friend came over?"
1.) From DenL4242:
Not a rule, but my mom washed bath towels after each use. I didn't know most people hung them up and used them repeatedly until I was in college.
2.) From InfiniteSandwich:
In order to stop tantrums on board game nights we played monopoly with the rule that you were allowed to go into debt. It wasn't until middle school that I learned the proper way. I'm still ashamed of insisting I hadn't lost while surrounded by all my dumbfounded peers. I must have looked like the sorest loser.