Floyd Mayweather didn't just throw shade at 50 Cent -- he threw EVERYTHING at the rapper ... including a piping hot bag of dirty laundry.
The on-again, off-again beef between the 2 is firmly back on, after Floyd shared a message on social media that began with ... "Curtis 'Confidential Informant' Jackson, you're mad because your oldest son Marquees mother doesn’t want to be with you! Your Son, your own flesh and blood don't want nothing to do with you!"
And Mayweather was just getting started.