Josh Brolin Thanos' Bare Ass is All Me ... But That's it for 'Endgame' Spoilers!!!

4/23/2019 12:30 AM PDT

Josh Brolin Jokes About Nude Thanos, Rebukes 'Avengers: Endgame' Spoilers

EXCLUSIVE

Josh Brolin's dropping his evil villain persona and showing off his playful side to talk Thanos' ass cheeks, and a major no-no in his book -- "Avengers: Endgame" spoilers ... just don't do it!

Brolin, who plays Thanos was at LAX Monday when we asked him about pulling back the curtain on a nude shot of his incredibly ripped, incredibly villainous character.

If you haven't seen it yet, it's quite a sight to behold ...

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Before the armor, a shower. #washingavengerscumoff #powerliftingantmansquish #APRIL26SPOILER

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Brolin insists the photo's all him -- from the busting veins to the muscular booty -- but based on who he says is training him these days ... we think he MIGHT be joking.

Anyway, where were we? 

Oh yeah, much like the film's directors, Anthony and Joe Russo, Josh is urging moviegoers to keep their mouths shut after they see it ... so as not to spoil the end of 'Endgame.'

Brolin warns those even thinking about ruining it for others -- especially east coasters who get to see the movie first -- they better snap out of it ... or face the wrath of Thanos.

Why test him? Those glutes and hammies mean business!

"Avengers: Endgame" comes out everywhere Friday, but the big red carpet premiere went down in L.A. at the Convention Center Monday night ... and the celebs brought their A game.