I'm going to make this dude sound really bad to some close friends
Why do you want to make him sound bad?
Because I want them to punch him in the face if they see him.
I understand that you might be upset with this person, but it is wrong to spread lies about other people, and to encourage causing them personal injury. Instead, you should just avoid spending time with that person since you don't like him.
I would never lie, I just left out a few details. He deserved it.
If the guy deserves anything, he will receive it in due time. By spreading lies, you are creating a problem where there is not one.