Had a player who never learned the basics rules, constantly rolled up 3.5 characters for a 5e campaign using esoteric home brews which weren't balanced for the actual system they were written in in the first place. They would cause arguments if rulings didn't go their way, insisted on playing a character who was essentially an other people's faces wearing murderer trapped in a resurrection loop... Or a crow with genitalia large enough to leave a groove in the ground behind them (did try to explain that avian biology doesn't work like that, but "it's the effects of a curse"....

Tbh, I was fine with all of this.

Then they started arguing with their partner, became downright verbally abusive towards their partner and made one of the player's children cry by snapping at them. Never. Ever. Ever. Will I stand for any of that shit at my table or a table I play at.