Ben Affleck wasn’t exactly out here saving Gotham -- more like saving himself from a full-body sweat-lodge meltdown ... all 'cause of that Batman suit, which he said made him sweaty AF.

The movie star spilled all the salty tea, saying those suits are built to look badass, but not to be worn by actual humans -- and you can sure bet that it was game-over for his comfort when that cowl went up over his head.

Ben got real with GQ about the Batsuit nightmare -- explaining the second you put it on, the perspiration kicks in. And since he’s already a majorly sweaty person, he was basically just pouring water.

He said the physical struggle matched the vibe -- he felt anything but heroic. All that heat, exhaustion, and nonstop sweat totally killed the superhero fantasy for him.

Affleck said maybe Christian Bale and Robert Pattinson had a different ride in the Batsuit -- but for him ... it just wasn’t it.

Ben suited up as the Caped Crusader in "Batman v Superman: Dawn of Justice," "The Flash, Justice League," and the extended cut, "Zack Snyder’s Justice League."

Looks like for Ben, the real villain wasn’t the Joker -- it was the damn Batsuit!