President Trump Condescends Greta Thunberg, She Trolls Him Right Back

President Trump's getting one-upped in his favorite arena -- Twitter -- by Greta Thunberg, or as he refers to her ... that kid with the "anger management problem."

The Prez took a pretty condescending shot Thursday morning at Time's Person of the Year. His reaction to her getting the honor ... "So ridiculous. Greta must work on her Anger Management problem, then go to a good old fashioned movie with a friend!"

And, for the coup de grace, he added, "Chill Greta, Chill!"

Well, the 16-year-old champion of the environment took Trump's advice ... in the most facetious way possible.

She straight-up jacked his tweet and slapped it in her Twitter bio, which now reads ... "A teenager working on her anger management problem. Currently chilling and watching a good old fashioned movie with a friend."