I'm going to go jump a kid who threatened to hurt my friends
Why don't you try to talk to the kid before beating him?
No, I'm not interested in talking to him anymore.
Responding to a threat of violence with violence will not solve anything. You & your friends need to talk to this kid. If he is still making threats after that, then you need to seek help from a responsible adult, like a teacher or even a parent.
What I do with this kid is my own business
It becomes other people's business if you or others get hurt.   It is best to keep out of trouble and settle it differently.