UFC fighter Joe Pyfer's elbow bent in a way no person's arm EVER should in his fight with Dustin Stoltzfus on Tuesday ... and it was so gruesome, Dana White nearly threw up ringside!

The disturbing injury all went down at DW’s Contender Series 28 ... where late in the 1st round of the Stoltzfus-Pyfer tilt, Pyfer was tossed and extended his arm to break his fall.

The problem? As Stoltzfus' weight crashed down on Pyfer ... his arm exploded outward -- dislocating at the elbow!!!

Here's the raw video -- but warning -- it's GROSS!

The fight was immediately waived off ... and the injury was so bad, when cameras cut to White, he was squirming in his seat and holding himself back from hurling!!!

Dana later commented ... saying, "I’m glad [Pyfer] only dislocated his elbow and didn’t break it on tonight’s Contender Series."

Despite the horrifying scene ... Pyfer took it all in stride -- he actually appeared to apologize to Stoltzfus and said straight up, "This sucks, bro."

YA THINK!?

Pyfer posted footage of himself in the hospital afterward vowing to come back.