Keep your 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.
See also: keep, on, shirt

Keep your shirt on!

 and Keep your pants on!
Inf. Just wait a minute! I'll be right with you. Keep your shirt on! Keep your pants on! You're next.
See also: keep, shirt

Keep your shirt on!

and Keep your pants on!
exclam. Just wait a minute!; Don’t be in a rush. (Possibly said as if to avoid a fight, for which one removes one’s shirt. That is, Let’s not rush into a big argument or fight; wait a minute. The expressions are old and in very wide use, too wide to suggest a reference to sexual urgency.) I’ll be right with you. Keep your shirt on! We’ll be there in a minute! Keep your pants on!
See also: keep, shirt