When you were a kid (or even a grown kid) and played Monopoly who put all the fines in a kitty which one would win by landing on 'Free Parking'? How about getting paid $400 when landing directly on 'Go'? You DO realize there is no reference to either practice in the actual rules - yet it is a common house rule. Also, who put properties up for auction when someone declined to buy? Nope, I didn't either - yet the official rules say this IS what you're supposed to do.
I only had one sibling so my brother would always create a dummy hand (which you could peek at one card when it was your turn) when playing Clue and probably incorporated a hundred other made up rules with several games to make accomodation for two players playing a multi-player game.
Who else made up their own rules or played games 'wrong'?