BAFTA Awards

A random dude crashed the stage at the BAFTAs -- where Christopher Nolan and other 'Oppenheimer' heads were after a major win -- and now ... the showrunners are pissed.

This awkward moment went down Sunday during the big British award show -- the Oscars, basically, for the UK -- and it happened right at the end of the show when 'Oppenheimer' won Best Film and a bunch of cast and crew members went up to accept.

CN obviously went up, as did Cillian Murphy and other producers for the film ... but there was one straggler who ran up onstage well after them -- and he definitely didn't belong.

The guy stood out like a sore thumb, just quietly standing in the back of the group and not batting an eyelash -- maintaining his composure and keeping up with the façade. Nobody said anything about him being there either ... including Cillian, who was right next to him.

The acceptance speech came and went, and this prankster didn't really cause much of a scene at all ... but that's not to say the BAFTAs people weren't angry, 'cause they were.

A rep for the org says ... "A social media prankster was removed by security last night after joining the winners of the final award on stage -- we are taking this very seriously, and don’t wish to grant him any publicity by commenting further."

They don't name him, but he's pretty easy to find online -- dude goes by the name of Lizwani ... and he does this crap pretty often. He's slinked his way into a number of award shows in Britain over the years ... and often documents it on his social channels.