I'm going to tell my coworker that adopting them into our team was a mistake
Why would you say that to a coworker?
It's impossible to deal with him, I can't stand his face and he pisses me off all the time
It's rude, and hurtful, to insult someone like that for any reason, even if they are annoying you.  You should treat coworkers with respect, and if you really can't work with them, you can change your working arrangements instead of just lashing out.
He deserves it.
You may not wish to work with this person any more, and if his performance is hurting the team, then you are right to try to have him removed.  However, making insults like the ones you just mentioned is highly unprofessional, and it will make you look even worse.  Since this will hurt your own career, I suggest just changing your work arrangements instead of trying to hurt this person.