Floyd Mayweather Buys 2nd Private Jet ... AND IT'S SICK!!

File under: "You know you're rich when" ... you buy a 2nd jet 'cause you're bored with the 1st one! That's exactly what Floyd Mayweather did ... snatching up a new private jet 2 weeks ago ... TMZ Sports has learned.

Floyd's rep tells us, "It’s a 12 passenger Gulfstream III with gold cup holders, gold sink, gold accents throughout. It has all white leather seats and a fully stocked kitchen. He now has two jets. Air Mayweather 1 and 2."

We're told similar planes can cost several million dollars -- but we don't know how much Floyd dropped on this particular jet.

Either way, it's good to be rich!!