“let your hair down”不是指“把你的头发放下来”，真实含义是放松一下；表里一致；放开些；尽情享受。

【例句】
Come on, Jim, this is a party! Let your hair down and go a little wild!
快点，Jim, 这是个派对。尽情享受, 玩得开心点！

Why don't you let your hair down? Come whenever it suits you.
你为什么不随便一点？只要你方便随时来吧。