let hair down

let (one's) hair down

To cease acting formally or conservatively; to ignore or relinquish one's inhibitions or reservations. Also worded as "let down (one's) hair." Come on, Jim, this is a party! Let your hair down and go a little wild!
See also: down, hair, let
Farlex Dictionary of Idioms.

let one's hair down

 
1. Lit. to undo one's hair and let it fall freely. When she took off her glasses and let her hair down, she was incredibly beautiful.
2. Fig. to tell [someone] everything; to tell one's innermost feelings and secrets. Let your hair down and tell me all about it. Come on. Let your hair down and tell me what you really think.
See also: down, hair, let
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs.

let (one's) hair down

To drop one's reserve or inhibitions.
See also: down, hair, let
American Heritage® Dictionary of the English Language, Fifth Edition.
See also:
  • let (one's) hair down
  • let one's hair down
  • let your hair down
  • let down (one's) hair
  • let one's hair down, to
  • part with
  • part with (someone or something)
  • give up the fight
  • give up the struggle
  • cancel out of (something)