In reply to a tweet by the Amazon founder touting the company's success despite its naysayers, Musk sent an emoji of a No. 2 medal, in reference to Bezos' current status as the world's second richest man. Musk reclaimed the top spot last month, becoming the third person to surpass the $200 billion milestone. At the time, Bezos' fortune was around $193 billion.
As of the time of publication Monday, Musk reigns supreme with approximately $203.6 billion, while Bezos trails behind with $189.7 billion, according to real-time tracking by Forbes.
In addition to the ongoing rivalry to become the world's richest man, the pair have also fought over supremacy in the space industry.
Blue Origin recently filed a lawsuit against NASA over its decision to solely award SpaceX a $2.9 billion contract, arguing the company received preferential treatment in the agency's procurement process for its Human Landing System program.
In addition to its lawsuit, Blue Origin released an infographic attacking SpaceX's Starship, claiming the spacecraft would be an "immensely complex and high risk" for NASA due to the fact that it has "never flown to orbit and is still being designed and could take as many as 16 flights to fully fuel before each lunar landing.
Musk has defended Starship's capabilities, arguing that while 16 flights would "not be a problem" it is "extremely unlikely."
"The sad thing is that even if Santa Claus suddenly made their hardware real for free, the first thing you’d want to do is cancel it," Musk fired back in a separate tweet.
Musk also criticized Bezos after Amazon's Kuiper satellite initiative filed a complaint against SpaceX's Starlink satellite constellation.
"Turns out Bezos retired in order to pursue a full-time job filing lawsuits against SpaceX …" Musk said.
Musk's latest jab comes as Bezos has arrived in West Texas ahead of Blue Origin's upcoming suborbital spaceflight, which will carry 90-year-old "Star Trek" veteran William Shatner, Blue Origin's vice president of mission and flight operations Audrey Powers, former NASA engineer and Planet Labs co-founder Dr. Chris Boshuizen and Medidata co-founder and Dassault Systèmes' Glen de Vries.
The flight, which will last for approximately 11 minutes, is slated to take off from Launch Site One at 9:30 a.m. Eastern Time on Wednesday after being delayed by weather.