At an online conference last October, doctors in Canada, France, the United Kingdom, and Hungary pooled their knowledge. They had all seen an increase in patients with this unusual form of tic disorder. One teenager came from the Pacific archipelago of New Caledonia, which France once used as a penal colony; another came from the tiny South Atlantic island of St. Helena, to which Britain sent Napoleon for his final exile. “Very remote locations,” Andreas Hartmann, a consultant neurologist at the Pitié-Salpêtrière Hospital in Paris, told me via email. “Yet accessible to TikTok, YouTube, and Instagram.”

Four months before the clinic in Hannover saw its first new-style patient, a 20-year-old German man named Jan Zimmermann had launched a YouTube channel called Gewitter im Kopf, or “Thunderstorm in the Head.” That’s how he describes living with his socially inappropriate, visually arresting symptoms: blurting out obscene words, throwing food, trying to nibble his friend Tim. In the past, he has set off fire alarms, pulled the emergency brake on the train, and once asked a cross-eyed HR manager, “Is the wall more interesting than me?”

Zimmermann now has 2 million YouTube followers and a bespoke app that allows users to download his “best tics” as sound files. On his merchandise page, you can buy hoodies, mugs, and a 25-euro doormat emblazoned with one of his most common sayings: Du bist heute besonders hässlich, or “You are particularly ugly today”—nearly the same phrase that kept coming out of Müller-Vahl’s patients.