David Otunga says he flew into "flight or fight mode" when he encountered the dude who broke into his car Monday night -- telling TMZ Sports, "I'm ready to tear this guy's head off."
Little backstory ... Otunga had finished a shoulder workout at his gym in Chicago when he saw a man inside of his car trying to steal his stuff, including Apple AirPods.
The WWE star says he freaked out at first, wondering if the guy had a gun -- but quickly realized the burglar was a coward who immediately began to beg Otunga to let him go.
"I go yoke him up and dude just starts pleading with me, 'No! I'm sorry! Please, don't hit me. Don't hit me, don't hurt me. I'm sorry, I'm sorry!'"
Otunga says the man claimed he was desperately in need of money and wanted to steal D.O.'s stuff, so he could sell it.
"I almost feel bad for him," David tells us ... "Like, I'm so pissed off, I'm ready to tear this guy's head off and then he's pleading with me."
Otunga says he ultimately shoved the guy and he ran off.
But, the scariest moment -- David says he later found the burglar's KNIFE in the car ... and quickly realized things could have been a lot worse.
"So, the dude had a knife and he could've stabbed me," David tells us ... "He coulda tried it. But, he didn't. I just thank God that it wasn't my time."