Brooks Nader might wanna log off and lie low ... because her ex, Gleb Savchenko, just went nuclear with a mortifying sex confession.

Gleb dished all to Dakota Mortensen on YouTube's "Unwell Winter Games" as they were bonding over "crazy" exes ... when he casually crowned Brooks the worst sex of his life!

He didn't stop there … claiming she was so full-on, all she wanted was make-outs and choking -- which he made very clear was not his vibe.

Still, according to him, that didn’t slow her down ... alleging she even pushed him up against a wall and chipped his tooth. 😬

Now here's the twist -- Gleb’s mostly kept quiet while Brooks did the talking on their messy, on-off romance ... spilling everything from their day-one hookup on S33 of 'DWTS' to accusing him of cheating.

But clearly, he had this one bomb he'd been sitting on -- and yeah, safe to say, this just took a sledgehammer to Brooks' man-eater rep.

We've reached out to Brooks ... so far, no word back.