What’s a weird rule your family had growing up that you thought was totally normal… until you grew up?

Using profanity was fine, so long as my sister and I didn't use it against each other, so long as we didn't use it any more than our parents did, and we could only use it inside the house. If we were caught swearing at school or something, we'd still be in trouble with them for it. Not all that weird, but definitely an unusual one.