Tucker, it depends on the level. In youth ball, I'm ejecting for any swear word, at any volume.
Do you mean that if direted at you, or heard at all? Kid catches his cleats in his laces, face plants, and blurts out something?
Last night, I had an assistant coach use a certain word (just me, HC, and him there) before the game. I tell him that if he says that during the game, he's done. Nobody else heard what was said.
I did need to clear a basketball court near my ball field 2 weeks ago because someone said F*** that loud enough for me to hear. HTHC told them to get out. (Later found out that he's retired BCoPD (Baltimore County Police).)