online argument; flame war
Internet slang for a heated back-and-forth argument, especially on social media like Twitter. Derived from 'response battle'.
from English res(ponse) battle
あの話題でレスバトルが始まった。
A flame war started over that topic.
彼はすぐにレスバトルに参加したがる。
He always wants to jump into online arguments.
Wasei-eigo from English 'response' + 'battle', referring to an online argument or flame war.