Diddy gives zero f****, and proved it with a Batman costume -- complete with a real Batmobile -- that's so dead-on to the 'Dark Knight' movies, it's sure to piss off Warner Bros. ... and maybe even SAG-AFTRA.

Check out the artist's killer look from Tuesday night's festivities -- the dude's a spitting image of the big screen Batman, and on top of his picture-perfect costume, he was riding around Hollywood in Batman's Tumbler ... the Batmobile of choice in the Christopher Nolan movies.

No clue how he got his hands on such an exact replica of the iconic ride, but it looks like he pulled it straight outta the Batcave.

As we reported, Diddy told Jimmy Kimmel he was going to step up his Halloween game this year -- after saying last year's insanely good Joker costume resulted in WB claiming it was a copyright violation.

Kimmel told him to just dress up as Heath Ledger's character again, despite the heat, but Diddy warned his costume this year would also have WB lawyers working overtime ... and he was true to his word.

And then there's the actor's union -- SAG said it didn't want its members dressing up as movie characters for Halloween, but Diddy, and several others, are clearly ignoring that demand.