let your hair down
US /lɛt jʊər hɛər daʊn/
UK /lɛt jʊər hɛər daʊn/
1.
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.
•
The party was a great chance for everyone to let their hair down.