Katt Williams Says Tiffany Haddish Only Famous 'Cause She Loves White Guys

Tiffany Haddish ain't s**t as a comedian ... is what Katt Williams is claiming after going on one of his patented rants, bashing her rise to success.

Katt joined V-103's 'Frank and Wanda' Friday and went nuclear on a bunch of comedians including Kevin Hart, Jerrod Carmichael and Hannibal Buress. But, he seemed to direct his most lethal shots at the "Girls Trip" star ... saying she's a stand-up hack.

Katt said Tiffany got famous off someone else's writing ... and ANYONE would have earned critical acclaim reading the "Girls Trip" script, which Katt claims he saw way back in 2004.

He added ... Tiffany's been in comedy since she was 16, but claims no one knows her jokes. Then there's this -- "She ain't done a tour yet. She ain't done a special. She has not proven the ability to tell jokes back-to-back for an hour to nobody."

For the record, Tiff has had specials and has a deal to do another for Netflix.

So, what's the secret to her success? According to Katt, it's just 2 words: Brad. Pitt. Watch ... he claims Tiffany's just playing the white card.