keyboard warrior

noun1

1. •
   (Internet, disapproving) A person who behaves aggressively or in an inflammatory manner in online textbased discussion media, but does not behave similarly in real life, potentially due to cowardice, introversion or shyness.

   • Others are newer converts who have only a vague idea how it all connects. There are law-abiding keyboard warriors as well as violent, unhinged radicals. — 2021