Stay frosty

[Justin Bieber]

(n.)A term meaning stay cool or stay calm. It is also used as a farewell to friends, and others.

[Sonia]

A valediction which has come to mean be cool, but which more properly understood is an admonishment to stay alert and on ones toes. See the quote below for the pop culture origin.

[Donald Trump]

To remain focused by not letting your emotions overcome you

[Jessica]

Earliest origin I have seen is the 1972 movie The New Centurions and is spoken by George C. Scott to the newbie Stacy Keach. The meaning is Stay cool and in control

[Mark Zuckerberg]

Military and or Law Enforcement jargon for Stay alert, or watch you back or be on your toes