Floyd Mayweather -- $100,000 Rainstorm ... In Miami Stripclub

There musta been storm clouds following Floyd Mayweather this weekend ... 'cause dude made it rain HARD in a Miami strip club ... throwing around $100k in cash ... and TMZ Sports has the footage.

Mayweather rolled into E11even to celebrate DJ Irie's birthday -- with a backpack that we're told contained $100k in greenbacks (Floyd was showing off some of the cash on his Instagram page earlier that day).

Our strip club sources tell us ... Jamie Foxx and Diddy were also in the building -- and at one point Diddy called every stripper down to the floor while the guys threw around fist-fulls of cash.

It's not like it's a big deal to them -- according to Forbes, Diddy is worth around $700 mil ... and Floyd made $105 mil over the past 12 months alone.

It's good to be rich.