Flavor Flav Booted From Rockefeller Center After CEO Murder Boosts Security

Flavor Flav Unexpected Tree-Lighting Visit ... Bypassed Heightened Security After CEO Shooting

Flavor Flav's all about fighting the power, standing up to NBC security ... but, it seems they were just doing their jobs -- 'cause we're told he wasn't expected at the tree-lighting, and security booted him.

Here's the deal ... Flav took to X to air some grievances about NBC kicking him out of the Backstreet Boys dressing room at the the Rockefeller Center tree lighting ceremony Wednesday night -- despite all his work with them during the Olympics.

However, sources tell TMZ security had a very good reason to kick him out of the event ... 'cause he wasn't on the list of expected attendees.

We're told Flav was at a party -- not affiliated with NBC -- nearby when he stopped in at the tree-lighting in Manhattan.

Our sources say security around the area was heightened because Brian Thompson -- the UnitedHealthcare CEO -- was gunned down about six blocks from where the tree-lighting took place ... so, they'd shut down much of the area to protect the tree lighting guests.

Despite this heightened security, it seems Flav somehow got past several layers of security into a holding area for the talent -- he's a charming guy, so it's not totally shocking.

This is when security realized he wasn't supposed to be there and, despite his celeb status, they quickly asked him to leave.

Our NBC sources tell us they're huge fans of Flavor Flav ... and, they'd love for him to attend the tree-lighting ceremony next year.

Worth noting ... Flav walked back his comments today -- putting the blame on the security guards who kicked him out, instead of on the network itself.

We've reached out to Flav about this new information ... so far, no word back.