How do some people manage to completely let loose?

I just came back from a holiday with friends and I’ve got to say I honestly don’t understand how some of them can let loose so easily – I mean shouting what’s on their mind, jumping around like hooligans, even in front of people they’ve only recently started dating…alcohol was often involved but even so I always keep this sense of self awareness, and whilst I wouldn’t want to be an immature twat, I do envy people’s ability to apparently let go of self awareness like that.

Have you guys got any insights or advice?