internet tough guy; keyboard warrior
Derogatory internet slang for someone who acts tough or aggressive online but is unlikely to behave that way in real life. Often used on forums and social media.
That forum has a lot of internet tough guys who immediately post aggressive comments.
He's a keyboard warrior online, but when you meet him in person he's very meek.
Compound of 硬派 (こうは, 'tough, hard-line') and 厨 (ちゅう, a derogatory suffix derived from 厨房 (ちゅうぼう, 'kitchen'), used in internet slang to mock someone as childish or obsessive). The exact origin is uncertain, but it follows a common pattern in Japanese net slang.