Last night Chris Brown and Rihanna were getting HOT AND HEAVY at NY's hotspot GRIFFIN. According to MULTIPLE SPIES - the two were in VIP together, along with TONS of other celebs - including Chris Rock, Dave Chapelle, Bow Wow, NFLer DeSean Jackson and rapper Meek Mill.

Well according to ONE snitch, Rihanna went to the PRIVATE RESTROOM - and she was followed in by CHRIS BROWN. The insider claimed, they were locked in the bathroom together for a long time, while both Rihanna and Chris' security stood guard outside the door.

When the two FINALLY came out, Chris exited first . . . and Rihanna came out second - looking NOTICEABLY DISHEVELED.

Pictures to come . . .