keep one's shirt on

[keep one's shirt on] {v. phr.}, {slang} To calm down; keep fromlosing your temper or getting impatient or excited.

Bob got veryangry when John accidentally bumped into him, but John told him tokeep his shirt on.

- Usually used as a command; may be consideredimpolite.

John said to Bob, "Keep your shirt on."

Contrast: GETONE'S DANDER UP.