Charlie was seen wearing orthodontic headgear in the episode "The Ballad of Steve McClean."
In the episode "The Fill-In", Charlie went on vacation with his mom, and had The Butcher (who had been friends with Charlie since elementary school) fill in for him. Dr. Two-Brains wanted The Butcher to team up with him, and for a while alienated his own henchman.
When The Butcher wouldn't team up with Two-Brains (who had built cheese shooters to allow him to shoot liquid cheese at people like how The Butcher threw meat), during a bank robbery, Two-Brains could be heard making fun of The Butcher, and when the meat man asked if he was being made fun of, the unnamed henchman, jealous, said "No, why would he make fun of you? He loves you."
Later, Charlie showed up with Exposition Guy (who thought he was a policeman) at the bank, and his nameless coworker was happy to see him.