A compound word from "instant" and "ban"; to be banned instantly, as from an online game or web forum.
A behavior for which there is zero tolerance, which will likely result in an instant ban.
As verb: You'll get an instaban for that if you're not careful.
As adjective: Posting child porn is an instaban.
1. Verb. To be banned for ongoing play in an online video game for some action of insignificance, typically by some fat power hungry nerd who thrives on exercising his online powers.
My boy Nameless One just got instabanned for saying google.com in the main chat room by faggot Adept_Lynx!