The always flashy Mayweather was in
Without missing a beat, Mayweather replied: "I don't even know who he is."
Previously, the professionally undefeated Rousey said she could defeat Mayweather in a mixed martial arts fight if she stayed close the ground.
"I would drop down to the ground and crawl over to him as fast as I can," Rousey said. "I would just be skittering after him like the one dude in 'Bloodsport' that was doing the whole monkey crawl fight system."
When reporters tried to explain who Rousey is, Mayweather insisted, "I ain't know who that is."
Rousey will appear this summer in "The Expendables 3" and next year in "Fast & Furious 7."
When he is not making bank in the ring, Mayweather is often up to something that draws attention.
Nicknamed "Money," Mayweather often flaunts his wealth via social media with pictures and videos of him buying expensive cars, riding in private jets, making outrageous sports bets and surrounding himself with huge piles of cash.
Mayweather is a moneymaker for others too.
His September 2013 bout against Saul "Canelo" Alvarez set records for highest pay-per-view gross ever at $150 million and highest live gate at $20 million, according to Forbes.
Mayweather made $105 million for 72 minutes of work in the ring, making him the highest paid athlete of 2014, Forbes reported.