godan verb (-ru), intransitive verb
lose one's temper; rage; flip out
Internet slang derived from the Korean term 火病 (hwabyeong, 'anger illness'). Used to describe someone suddenly exploding in anger online, often in a dramatic or over-the-top way. Sensitive term; may be considered derogatory or mocking.
See also: 火病
あのユーザー、ちょっとしたことでファビョってたよ。
That user flipped out over a tiny thing.
ファビョる前に深呼吸しよう。
Let's take a deep breath before losing it.