SuperBrony87

Well when you think of it he was a hat maker and hat makers suffer from mercury poisoning and other chemicals used in hat shops. Often called "The Mad Hatter" disease. SO he's really not that mad it's not his fault his is a hazard of his occupation. I can't speak for what the other un usual characters have... Like Tweedle Dee and Tweedle Dumb or that March Hare or that cryptic Cheshire Cat.

Other symptoms of the Mad Hatter Disease includes: shaky hands, which is referred to in many places. mainly the "hatter shakes" in Russia and France AKA the "Danbury shakes" from Connecticut. Inorganic Mercury was used for the felt in hats.