keep your hair on
/ˌkiːp jə ˈheər ɒn/idiom
used to tell someone to calm down and not get angry
не кипятись, успокойся
Русский аналог: «не кипятись»
Шутливое и разговорное.
“Keep your hair on! It was only a joke.”
“All right, keep your hair on — I’ll do it now.”
“Tell him to keep his hair on.”