Chris Brown and Rihanna -- DATE NIGHT at Jay-Z Concert

Rihanna and Chris Brown aren't even trying to hide it anymore -- 'cause it looks like they were getting cozy at the Jay-Z concert tonight ... and, based on Twitter, everyone in Brooklyn saw it.

A pic taken from behind RiRi and Chris at Barclays Center is burning up the Internet -- they're seated in VIP ... he's on the left, she's on the right.

No physical contact -- in the photo, anyway -- but Chris' right arm is stretched around the back of Rihanna's chair.

This reunion comes the night after Chris and Rihanna were spotted at the same table in an NYC nightclub.

They were also seen leaving the same hotel on Wednesday -- and, for what it's worth, Chris' blind-as-a-bat GF Karrueche tweeted "Bye baby" ... just a couple hours before tonight's concert.

Apparently, Jay-Z is so powerful he can turn back time ... to 2008.