We did tell him to cool it but he just got more and more irate: he ended up hitting him.
Or Be Cool Mellow Out Calm down or stop what you're doing "Hey can you cool it with the music, I'm trying to mellow out "
(Slang) calm down, take it easy; stop it (i.e.: "As soon as he enters the room, cool it you guys")
become quiet or calm, especially after a state of agitation; "After the fight both men need to cool off "; "It took a while after the baby was born for things to settle down again "