let your hair down

US /lɛt jʊər hɛər daʊn/
UK /lɛt jʊər hɛər daʊn/
"let your hair down" picture
1.

くつろぐ, 羽目を外す

to allow yourself to behave much more freely and enjoyably than usual and relax

:
It's good to let your hair down after a long week of work.
長い一週間の仕事の後でくつろぐのは良いことだ。
The party was a great chance for everyone to let their hair down.
パーティーはみんながくつろぐ絶好の機会だった。