President Donald Trump lashed out at 16-year-old climate activist Greta Thunberg on Thursday, a day after she was named by Time as its Person of the Year, calling her selection “ridiculous.”

Axar.az reports citing AP news that the Swedish teen has become a symbol of a growing movement of young climate activists after leading weekly school strikes in Sweden that inspired similar actions in about 100 cities worldwide. She has drawn large crowds with her fiery appearances at protests and conferences over the past year and a half.

In a Thursday morning tweet, Trump said, “Greta must work on her Anger Management problem, then go to a good old fashioned movie with a friend!”