I feel I have to post
I gotta say I've never been bullied, and Im really not the "cool guy" type, so I guess Im lucky to not know how you feel.
Now, onto the more funny side, I'd say physical violence ain't got shit over psychological trouble you can do to someone. What you want to do is fuck with them, but over a long period of time. I'd suggest to make them paranoid. When they are by themselves drive-by them and shoot them with blanks... or whatever for that matter, bb gun who cares. All you gotta do is scare the shit out of them. I'd suggest repeating the whole thing over quite a bit of time, make them look behind their back continually. I believe that will seriously fuck them up.
If I was you, I'd rather have them have everything go wrong at once than getting beaten. Mail shit to their moms about how they abuse drugs, someone suggested sending fake anonymous letters to their girlfriends.. Make everything they have turn back to them.
I remember reading somewhere else, a similar situation than yours and someone suggested to put an axe in one their car door, something along those lines.
I also remember a video from a few years ago, where 3-4 guys would put dog's poo in socks and then hit the people's house at like 4 am with the socks, there was poo all around their house within a minute, plus the shock of getting waked up by some heavy banging too.
So yeah, if I was you, I'd rather do several smaller psychological attack and fuck their mind up, until where they can't go outside without being paranoiac.