50 CENT GOOD LUCK GETTING A HIT FROM DIDDY!

50 Cent threw enough shade to keep Diddy cool for a few months when he begged a packed Scottsdale club to rattle off the Bad Boy honcho's last hit track.

Let's just say there were a lotta crickets inside INTL Nightclub over the weekend.  

Someone does eventually offer up Diddy's "You Could Be My Lover" off his most recent "MMM" mixtape -- and Fiddy performed a mocking lip sync.

There's been beef between Fif and Diddy for more than a year now -- most of it one-sided as 50 keeps throwing social media jabs over music, their vodka lines, age, weight and just about everything else.

Diddy rarely responds, but once again ... ball's in his court.

Me and PUFF sat and kicked it today he said, 50 I'm getting to old for this sh!t. I said I KNOW