Let your hair down
Definition 1 of 1
Pro Tip 1/3Informal Situations
Use 'let your hair down' in casual settings among friends, not in formal or professional environments. 
Come on, it's the weekend! Time to let your hair down!
Pro Tip 2/3Figurative Meaning
'Let your hair down' isn't about hair. It's an expression meaning to relax and be less formal or serious. 
After the exams, Sarah decided to let her hair down at the beach party.
Pro Tip 3/3Positive Connotation
The phrase usually suggests positive feelings like relief or freedom from stress. 
We can finally let our hair down now that the project's complete.