Paris Hilton Loves Mayweather's $18 Mil Watch, 'Looks Like One That I Have!'

50 Cent said Floyd Mayweather is a FOOL for snatching up an $18 MILLION diamond watch -- but Paris Hilton tells TMZ Sports ... Fiddy is wrong, she actually likes it!!

"It looks like a watch that I have actually," Paris said at LAX.

Floyd claims he picked up the famous "Billionaire Watch" from a jeweler in Japan -- a watch that contains 239 huge diamonds!!!

50 Cent clowned Floyd for the purchase -- saying, "Man they done found the 1 fool in the world,dumb enough to buy that watch. LOL get the strap."

As for Paris, she defended Mayweather's spending habits, saying -- "It's a lot ... but I think he works very hard, he works for his money and he can buy whatever he wants!"