Yk Perry was in the anger managment class
based on the fact that that class was to make someone get angier, not less angry, Im starting to think perrys trying to find ways to make himself seem unhappier so people will take him seriously.
Or maybe he does have trouble expressing his anger, when hes constantly being beaten and exploded he doesnt often fight back.
he only really did in one scene when he ranting about gart, and that mightve actually taken place after the anger management class, Because the episodes are anything but chronological.
Also wouldnt it be crazy if perry used to bottle up his emotions, and smile in the face of uncertainty so much, (not much different to monster) that it caused his mouth to rust in place from underuse? Not my official headcanon but its fun to think about.
Orr maybe Im connecting dots that were never there in the first place, but who knows.