keep one's shirt on

keep one's shirt on  {v. phr.},  {slang}
To calm down; keep from losing your temper or getting impatient or excited.
Bob got very angry when John accidentally bumped into him, but John told him to keep his shirt on.
- Usually used as a command; may be considered impolite.
John said to Bob, "Keep your shirt on."
Categories: {slang} {v. phr.}