I can think of several off the top of my head.
1) The whole catcher being able to block home plate in baseball and the runner allowed to truck him. Way too many injuries and potential for injury. What makes home plate any different than any other base?
2) Hand-checking in the NBA. These dudes are huge, athletic, and the game is being slowed down. These stupid hand-check fouls are ruining the game because of how easy quick point guards can just drive on every possession and either score or earn free throws.
3) Fighting in the NHL. It's not allowed in any other sport, it shouldn't be allowed in hockey either for obvious reasons. If there is a fight, a 5 minute major isn't enough.
4) In the NBA, I think a player should get an assist if he passes the ball to a teammate, that teammate gets fouled, and hits both free throws.
What do you guys think? I'm bored and just drank a few Stella's. Only reasons for this thread being started.