Wiktionary
go postal
vb. (context intransitive chiefly US informal English) To behave in a hysterical, angry or irrational manner.
Usage examples of "go postal".
He opened it to the sketch that had made Cherner go postal, the drawing copied from Ben Feinman's blotter.
If they blew circuits all over the fleet, like last time, Kolhammer would go postal for sure, and that sort of footage could keep a guy entertained for months on a long voyage.