Twitter owner Elon Musk hit Facebook founder Mark Zuckerberg below the belt in their social media word war, commenting "Zuck is a cuck" in a tweet.

Musk ramped up their online spat following the launch of Zuckerberg's Threads app, touted by netizens as a "Twitter killer".

In a follow-up tweet, Chief Twit proposed a "dick measuring contest".

To recall, both tech titans have agreed in principle to a cage fight at the UFC octagon in Las Vegas.

Meanwhile, Elon Musk (Parody), a verified Twitter account, posted: "I can't wait for this dick measuring contest. I will win. Get your rulers out."