Twitter owner Elon Musk has suggested he and Mark Zuckerberg should have “a literal dick-measuring contest” in the latest broadside aimed at his rival billionaire.

In a message inspired by the Meta chief executive’s launch last week of Threads, a Twitter competitor, Musk added a ruler emoji.

Using a slang word for “cuckold”, popular in rightwing circles as a term of derision, he also wrote: “Zuck is a cuck.”

By Monday, Threads had reached 100 million users, according to the website Techcrunch.

Twitter has about 250 million active users but it has been battered by controversy and technical problems since Musk, the man behind Tesla and SpaceX, bought it last year, for $44bn.

Twitter’s website traffic is also “tanking”, according to the chief of the internet services company Cloudflare, amid signs users are migrating to alternative platforms such as Threads, BlueSky and Mastodon.

Launching Threads, Zuckerberg said: “The goal is to keep it friendly as it expands. I think it’s possible and will ultimately be the key to its success.

“That’s one reason why Twitter never succeeded as much as I think it should have, and we want to do it differently.”

Musk has also proposed a mixed martial arts bout with Zuckerberg.