Floyd Mayweather says his friend Donald Trump's infamous "grab them by the p***y" comment is no big deal ... because Trump was just talking like a "real man."

Floyd appeared on the "Hollywood Unlocked" show when he was asked about the leaked Access Hollywood video from 2005 -- you know the one.

Floyd agrees with Trump that it was just "locker room talk" ... and explains how the language Trump used is simply how "real men" speak to each other.

"Real men speak like, 'Man, she had a fat ass. You see her ass? I had to squeeze her ass. I had to grab that fat ass.' Right? So he talking locker room talk."

"I’m the man, you know what I’m saying? You know who I am. Yeah, I grabbed her by the p***y. And?"

Bottom line -- Floyd thinks Trump was just keepin' it real.