keep shirt on
keep (one's) shirt on
To remain calm and wait for something. Typically used as an imperative in the phrase "keep your shirt on." Keep your shirt on, dude, the pizza will be here soon enough. It would have gone smoothly if Larry had been able to keep his shirt on instead of trying to get in early.
keep one's shirt onand keep one's pants on
Fig. to be patient. Wait a minute! Keep your shirt on! Keep your pants on! I'll be with you in a minute.
keep (one's) shirt onSlang
To remain calm or patient: The plane doesn't land for another hour, so keep your shirt on.