Ronda Rousey says Floyd Mayweather should get in touch with her "when he learns to read and write."
Her dig is the latest addition to a rivalry between the two top fighters, with both of them claiming to be better a better fighter and more successful than the other.
Rousey has also called Mayweather out on his history of domestic violence, saying she wondered how he felt "getting beat by a woman this time" after she won Best Fighter over him at the ESPY awards in July.
Mayweather said when Rousey made "US$300 million a night," she could give him a call.
Rousey hit back: "I actually did the math, and given the numbers of my last fight ... I think I actually make 2-3 times more than he does per second," she told TMZ while walking her dog. "So when he learns to read and write, he can text me."
Pressed on whether she makes more per second than Mayweather, Rousey said, "Yeah, I'm just more efficient" than he is.
Rousey's latest three fights total 96 seconds of action and her speed in knocking out opponents is becoming legendary.
Earlier this month, Mayweather said for Rousey to call him when she makes $300 million in 36 minutes, presumably referring to his take from his megafight with Manny Pacquiao earlier this year.
That comes out to be $138,888.89 per second for Mayweather.
The figures from Rousey's 34-second win over Bethe Correia at UFC 190 have not been revealed, but if she made two to three times more per second than Mayweather, Rousey would have come away with a paycheck somewhere between $9.4 million and $14.1 million.