Floyd Mayweather -- 'Man, Let Nick Diaz Smoke Weed!'

Floyd Mayweather was downright flabbergasted when he learned UFC star Nick Diaz had been suspended for 5 years after testing positive for weed ... and his reaction was all caught on video.

Floyd was talking to the Mayweather Boxing Channel when he was informed about the punishment handed out by the Nevada State Athletic Commission ... and responded:

"HUH!?!?"

He continued, "Man, let that man smoke weed and enjoy his life."

Finally, Floyd and Ronda Rousey are on the same page ...