1) To be so extremely angry, that your anger can only be done justice by comparing it thunder.
2) Not any sort of normal anger, this is a special type of anger that people feel often when they get so pist that their words and sentences become incomprehensible or they begin to foam at the mouth.
1) I can't believe that cunt ass howler monkey
gave us the test today, imma be thunderpist if I fail that shit.
2) What that ho said to me earlier got me straight thunderpist man, I'm surprised I didnt smack a tooth out that bitch's mouth.