The feud between 50 Cent and Floyd Mayweather is still going -- Fiddy just CLOWNED the boxer's newly announced fight, saying his opponent is more "Uber driver" than contender.
As we previously reported ... Mayweather just signed a deal to fight on New Year's Eve in Japan against an undefeated 20-year-old kickboxer, Tenshin Nasukawa.
Unclear whether the bout will be a boxing match or full-on MMA ... but, either way, 50 says it's a joke.
"Champ fighting a Uber driver before the IRS embarrass him again. Pay preview my ass, we watching this on YouTube."
50 didn't stop there ... sayin' Floyd shoulda taken on Gennady Golovkin -- writing, "What happen to GGG, couldn't find his phone number. get the f**k outta here wit this sh*t."
50 added, "Champ done turned into a circus act ... at least Canelo fighting killers."
Fitty and Floyd have been beefing on social media for months ... with Mayweather recently saying a rift between the rapper and Floyd's manager, Al Haymon, is where the tiff all started.
50 seemed to extend an olive branch to Floyd in a post back in July ... callin' Money his "brother" -- but, clearly, no beef's been squashed here.