Boxer Shannon Briggs -- Fight with Wladimir Klitschko Was Real ... 'He's a Punk'

Former heavyweight boxing champ Shannon Briggs says his hostile encounter with Wladimir Kitschko this week was 100% REAL ... telling TMZ Sports he LOATHES the guy and wants to set up a fight, STAT.

Footage of Briggs crashing Wladimir's workout in South Florida this week went viral -- with Shannon getting right in the Ukrainian legend's face to challenge him to a brawl.

"I went there to fight totally for free ... with no gloves," Briggs says ... "He's a punk."

So, where does the hostility come from? Briggs says Wladimir dissed him in public a few years ago for no reason -- treating Briggs like a nobody outside of a random event.

Now, Briggs says he feels like the only way he can let that go is if he gets the chance to pound Wladimir's face into a jelly.

"I'm putting pressure on him daily. He's going to fight me or leave this country. I came back to boxing just to whoop his ass."