Boxer Floyd Mayweather and UFC champion Conor McGregor may never step into the ring—or Octagon—together, but they’ve done enough fighting over social media to fill a pay-per-view card.

This time the battle is over money—the one area where Mayweather can throw a knockout punch. And that’s exactly what he did on Twitter.

The boxer taunted McGregor in their latest back-and-forth with a picture comparing the net worth of the two stars:

Mayweather and McGregor—and UFC president Dana White—have all thrown out their opinions on a potential fight between the stars, but an actual bout is looking unlikely. White said he would be willing to pay $25 million for Mayweather to battle McGregor, but the boxer scoffed at that number and then took a few shots at White, saying he used to “carry his bags.”

The idea of a Mayweather-McGregor fight may be more fun than an actual bout, but if enough money gets thrown on the table, anything can happen.

In the meantime, the best fight between Mayweather and McGregor likely will be on their social media feeds. Keep an eye on those.