Justin Bieber -- REJECTED by NYC Nightclub

Poor little Justin Bieber wanted to party his face off Monday night ... but His Douche-ness was brutally shot down by one NYC nightclub ... because he's still a baby in bar years (i.e. under 21).

Our NYC party sources tell us ... Biebs and his crew showed up to Griffin Nightclub in the Meatpacking District around 2:00 AM ... looking to drop serious coin on bottle service.

But money can't buy everything ... we're told JB was DENIED entrance by the club's security because he's only 19 -- making his presence a potential problem (see Chicago earlier this month).

Not to be defeated ... Biebs and his posse were shot minutes later cruising into another club, Catch ... where he probably just sipped water.