Postal
To refer to someone who's gone to a level of insanity, (Usually from being treated like really terribly) That they become a psycho and may end up harming someone, the term got popular from the Postal game series
Guy 1: I'M GONNA KILL YOU, YOU SON OF A WHORE I WILL GUT YOU AND YOUR FAMILY!!!
Guy 2: HE'S GONE POSTAL!
Guy 2: HE'S GONE POSTAL!
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