Someone sent me this meme about rock-paper-scissors the other day:
Spoiler

Which reminded me that a common German "house rule" in this game introduces a fourth shape, the well. It beats scissors and rock but loses against paper (the logic being that paper covers up the well, while scissors and rock fall down in it), and it is made using this sign:

When I was first introduced to this game as a child, we were using the well too, but it is pretty obvious that this is a very stupid rule. For one thing, it creates uneven odds, with two "good" shapes winning against two and losing against one, and two "bad" shapes losing against two while winning against one. But that in itself wouldn't be much of a problem if it was properly balanced, it could even add some depth to the game.
No, the real problem is that the rock becomes completely obsolete. While scissors still have use as being "anti-paper", rock does absolutely nothing that the well can't do, so a smart player would never pick rock, thus effectively turning the game into well-paper-scissors, which is absolutely pointless.
But yes, that's how this game was introduced to me. We didn't question this stuff back then, it still kept us busy on long car trips, for a few minutes.