"When will this guy expend all his cred?" Drew Dickson, founder of London-based Albert Bridge Capital, wasn't impressed by Elon Musk's Twitter activity last week, and one can see why.

Musk's tweets have been driving huge moves in the cryptocurrency markets in recent months. Occasionally they are serious, as was the case when Musk said Tesla would no longer accept bitcoin as payment due to environmental concerns regarding its energy use.

Mostly, however, Musk is joking around, posting cryptic tweets like “How much is that Doge in the window?” that nevertheless catalyse major moves in dogecoin and other cryptocurrencies.

Dogecoin started as a joke, but the fortunes being made and lost in the cryptocurrency markets are no laughing matter. Musk’s tweets are increasingly irresponsible, given he knows they will trigger serious price moves.

Tesla shareholders, too, might prefer if Musk stopped messing around. Tesla shares have lost over a third of their value and recently fell below their 200-day moving average for the first time in nearly two years.

As Bloomberg's John Authers has noted, Musk risks "turning himself into an unserious figure", an "entertainer" – not a good look for someone who is, after all, head of one of the world's biggest companies.