let your hair down
US /lɛt jʊər hɛər daʊn/
UK /lɛt jʊər hɛər daʊn/

1.
放松, 尽情玩乐
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.
辛苦工作一周后,好好放松一下是很好的。
•
The party was a great chance for everyone to let their hair down.
派对是大家放松一下的好机会。