keep your panties on
An expression used primarily in the southern U.S. to tell someone who is acting impatiently to calm down.
Person #1: Ya'll best be fixin' to get them fences up 'fore I get mind to tan your hide!
Person #2: I reckon you keep your panties on, darlin', or you gon' get madder than a wet hen!
Person #2: I reckon you keep your panties on, darlin', or you gon' get madder than a wet hen!