to let (one’s) hair down (to relax and enjoy oneself)
A: Are you going to the party tonight?
B: Of course. I’m going to let my hair down and have fun!
A: You work too hard. You should come out with us tonight and let your hair down.
B: I wish I could, but I’ve got to finish this report before tomorrow.
How about you? Have you let your hair down recently? Where did you go?