Usain Bolt -- Slappin' Dat Ass ... At Miami Nightclub (VIDEO) -

FAST HANDS

What did the 5 fingers say to the butt? SLAAAAAP!!!

That's how it went down for Usain Bolt at FDR nightclub in Miami this weekend ... when a hot chick in a thong started grinding up on the fastest man on the planet during Lil Wayne's birthday bash.

Check out the footage ... Bolt and his crew were showering some of the club's lingerie dancers with cash -- seriously, money was spillin' out the panties -- when Bolt decided to throw in a little smack for good measure.