To become aggressive and erratic, especially due to stress; specifically, to carry out a shooting spree at a workplace environment; also (more generally) to become very angry; to lose one's temper.
throw one's toys out of the pram
verb
To lose one's temper; to throw a tantrum.
How often have the words go postal and throw one's toys out of the pram occurred in a corpus of books? (source: Google Ngram Viewer )