In general: to leave behind
one's inhibitions or to behave in a
way that is free from
social limitations or any code of conduct.
(to let
one's hair down)
Corrine Bailey Rae, Song:
Put your records on
Girl, put your records on, tell me your favourite song
You go ahead, let your hair down
Sapphire and faded jeans, I
hope you get your dreams,
Just go ahead, let your hair down.