Deliberate mispelling of the word 'fanboy' typically referring to an annoying, immature fan of a specific video game console.
fanbois typically spend most of their free time telling anyone who will listen how perfect thier console of choice is, and how inferior all other products are. fanbois will not stop annoying other people until everyone they know is converted to their way of thinking.
neutral observer: "Console X looks to have a strong line up this year, but console Y still has the momentum from last year"
fanboi: "NO STFU CONSOLE Z IS THE BEST EVER. UR ALL IDIOTS, GO WASTE MORE MONEY ON YOUR SHIT CONSOLE X AND Y LOL"
fanboi 1: well well, if it isnt mr stupid console Y owner fanboi 2: your just jealous of how awesome console Y is
*fight to the death*