Usually the problem players self-boots themselves. They'll reveal themselves to be incompatible with the rest of the group, act oddly, & announce (with varied degrees of drama) that they're quitting.
Sometimes though we have to break the news to someone that we're dropping them.
The most recent player we had to do this with was a high school kid (17? 18?) who had joined our ToA game at the local shop.
I can accommodate up to 7 players, so I don't have anything against adding brand new players to my shop game as long as there's an open chair. And we get a fair # high school students rotating through who can only stay for about 3/4 of a session. That's OK, we understand. So you can't die in my game unless you're present & we'll give you a quick recap of what you missed next session.
This kid though....
He wouldn't bother to read/understand the rules,
He cycled through characters at the rate of about 1 per session due to getting them killed - because he wouldn't understand the rules, this led to constantly having to work a new character in.
He'd get pretty angry when the rules he refused to understand (that everyone else is playing by & trying to explain to him) prevented his actions/success,
He proved fairly obnoxious & foul mouthed,
Paid little attention to anything other than whatever he was concerned with atm (including the recap of what he'd missed last time when he had to leave - but was always asking what was going on/what he'd missed),
And he never shut up. He would just over talk anyone, any time. Often about things completely unrelated. Didn't matter if they were already speaking or what they were saying.
After about a month & a half of this the other players had had enough. So one session after he'd lost yet another random character & left we decided it was time for him to go.
A few days later when I saw him there at the shop & just told him straight up that the group wasn't enjoying playing with him, why, and that he wasn't invited back to the game.
I suggested that he look into joining one of the other games being run at the shop (there's 3 or 4 other groups)
His response was "Oh, Ok."
Since then he's been booted out of every other RPG game & is only accepted by the Pokémon players (who are a really mixed lot to put it politely)