Now THIS is a debate -- the race for Sheriff in Florida's Palm Beach County has one candidate so fired up, he said what's really on his mind after getting roasted in a showdown with his rivals.

The debate went down by Zoom earlier this week, and Michael Gauger didn't mince his words ... firing back at fellow candidate Lauro Diaz by calling him a "f***ing ***hole!"

It all kickstarted when Diaz completely bypassed the other candidate, Alex Freeman, to declare the race was a two-man show, with his sights set squarely on Gauger.

Diaz criticized Gauger by claiming he was the main culprit behind all the problems the community's facing, because he'd spent 51 years in the Palm Beach County Sheriff's Office before retiring in 2021.

While Diaz was talking, Gauger was visibly angry ... picking up a pile of paper and slamming it on the table out of frustration. At one point, he got so flustered he was almost out of frame but composed himself, waiting for Diaz to finish before dropping the f-bomb.

You can see Diaz and the other candidate, Freeman, reacting with a mix of shock and awe ... before the moderator tried to restore order.

Gauger tells TMZ he thought he was muted and believed his personal video wasn’t available after he switched to his phone when the Zoom link wasn’t working on his iPad.

Classic 2020, mid-pandemic mistake, really.

He adds ... he was so frustrated by Diaz, he muttered the comment, thinking it was just a private expression. He also insists he doesn't normally use that kind of language in public, and he's apologized for it.