That's Bone Collector -- the street ball legend who put Floyd Mayweather on his back Monday -- telling TMZ Sports he still can't really believe he crossed up The Best Ever!

"Floyd Mayweather is the richest ankle I've ever collected," Bone tells us. 

Of course, Bone's highlight at the $50k Charity Challenge celebrity basketball game has gone super viral ... everyone's praising the only pro athlete to ever drop Mayweather in any sport, EVER!

So, how did Floyd react after the embarrassing fall? Bone says the guy acted like a true pro -- he got up and continued to ball out. 

"He came back and played hard," Bone says ... "After that it was more of a mutual respect thing."

Bone says he kinda feels bad for Floyd because the two are good friends and he didn't want to humiliate the guy ... but on the other hand he's LOVING all of the praise he's getting!

In fact, Bone says everyone from Snoop to Nate Robinson to Rob Gronkowski dog-piled on him after the move in one of the coolest moments of his life.