Suge Knight -- 'Bitch Ass' Diddy Knows I Didn't Murder Tupac ... 'Cause Tupac's Alive!

Suge Knight just fired a metaphorical shot at P. Diddy ... telling us he's a "bitch ass" who should be getting more heat for plotting to kill Tupac Shakur.

Suge was leaving 1Oak last night when he unleashed a rant about the Tupac shooting, saying ... "Everybody know off the top, I ain't the n**** killed Tupac. I'm the n**** protected Tupac!"

Then he points a finger directly at Diddy -- "Bitch ass Puffy can get him a mutha******* star (on the Walk of Fame), and every rat in the world say he's the one who killed Tupac, or had him shot."

As for why no one's been charged in 'Pac's death -- even though an inmate confessed in 2012 -- Suge's explanation is simple ... "Tupac's not dead!"