One of mine (I have many yay neurodivergece) is when people say the phrase "a broken clock is right twice a day". The phrase is actually "a stopped clock is right twice a day." A clock that is stopped will definitely be right twice a day but a clock that is broken could be right multiple times a day or not at all depending on how it's broken. Maybe it's just a little slow running in which case it'll never be right. Maybe it's spinning wildly out of control so it'll be right a lot but still useless.
It annoys the shit outta me and it is so dumb it definitely should not. Anyway your turn.
Baseball specific one: "ground-rule double" colloquially used almost all the time to mean "automatic double." If a batted ball bounces on the warning track and goes over an outfield wall, it's an "automatic double," that's what it's called in the rulebook and that's a universal rule regardless of what ballpark the game is played at. "Ground rules" are specific to the ballpark, like a ball getting stuck in the ivy at Wrigley Field, or the catwalks on the dome in Tampa. One of those catwalks is a ground-rule home run, but nobody ever says that. For some reason, "ground-rule double" is ubiquitous for automatic double, but actual ground-rule stuff is very rare.