They “let it all hang out” quite literally.
https://en.wiktionary.org/wiki/let_it_all_hang_out
> (idiomatic) to relax and be carefree
> Synonym: let one's hair down
alt Hacker News
https://en.wiktionary.org/wiki/let_it_all_hang_out
> (idiomatic) to relax and be carefree
> Synonym: let one's hair down