Go postal
Definition 1 of 1
Pro Tip 1/3Origin Story
Originates from US postal worker incidents in the 1980s-1990s where workers became violent. 
The phrase 'go postal' dates back to a sad period in US history.
Pro Tip 2/3Informal Usage
Used informally, often in casual conversation, but can be inappropriate in formal situations. 
My friend was about to go postal after losing his keys again.
Pro Tip 3/3Negative Connotation
Carries a negative connotation, implying harmful loss of control or unprofessional behavior. 
The manager warned the team not to go postal during the stressful project.