keep your hair on
keep (one's) hair on
To remain patient and calm, especially when beginning to become angry or upset with impatience. Usually said as an imperative. Primarily heard in UK. Yeah, yeah, keep your hair on! I'll have the report finished by the end of the day! A: "That lady is pestering us about getting her car back today." B: "We need another day to get it fixed. Tell her to keep her hair on!"
keep your hair onBRITISH, INFORMAL
If someone tells you to keep your hair on, they are telling you in a forceful way to calm down and not be angry or impatient. `All right, keep your hair on,' Ralph said with a shrug. Note: The usual American expression is keep your shirt on.