That's Floyd Mayweather showin' off his INSANE car collection at his Las Vegas mansion ... a garage filled with 16 cars -- including 5 Rolls-Royces!!!

The undefeated boxer uploaded the video tour Friday ... saying he needed help picking a ride to drive over to his gentlemen's club, Girl Collection.

"I don't know what I wanna take out tonight," Mayweather says.

And, here's what's in his garage ...

5 Roll-Royces, 4 Ferraris, a Mercedes McLaren, a G-Wagon, a Bentley coupe -- plus the truck AND car version of the Lambo and Maybach!

"I got about 100 cars but right here -- we like to call this the Sweet Sixteen!"

He finally ended up picking the Maybach (the car version) to "make things nice and easy."

FYI, this Vegas mansion is gorgeous too ... he gave a tour last June, revealing his library-like closet filled with red bottoms to the indoor pool and spa.

Just another day of Mayweather reminding us how rich he is -- the guy just made $100M fighting Logan Paul in June ... and has generated $1.6 billion in revenue in his career.