abusive or insulting online is called
Early on in the age of the internet and chat rooms, the word flame began to be used to describe abusive messages.
Flames
abusive or insulting message
An invective is a highly insulting or abusive piece of language.
Using or containing insulting or coarse language
Flame mail refers to angry, hostile, or abusive emails or messages sent to someone with the intention of insulting, criticizing, or belittling them. It often involves harsh language, personal attacks, or threats, and is typically delivered in an aggressive or confrontational manner.
A player may be sent off for using offensive, insulting, or abusive language [toward anyone].
abusive
Draco called Hermione a mudblood - an insulting term for muggle-borns.
It is usually referred to as cyberbullying.
It might be called a rant.
(abusive answer deleted)