A "Gabi" is obsessed with an anime character and will fantasize about being with him or her because they can not find anyone real to be with. Along with this comes TERRIBLE drawings of this character but the Gabi insists that she (or he) is a great artist, and belives that people actually enjoy looking at this flat anatomy-less garbage that they spew out onto paper.
Quite often a Gabi will shoot down artists who have amazing work, insisting that she (or he) is the best, and sometimes they will go as far as too steal art from other people, if they finally realize that their own creations are pathetic.
Apart from that a Gabi will also normally act a complete bitch, and will always attempt to one-up anybodies sad stories insisting that her (or his) life is the worst and that nobody could have it worse than she's (or he's) had, ect.
In short; Gabi is a term used for a self centered bitchfuck, who is obsessed with anime and can not, and will never be able to create a decent piece of art.
You: Yeah, so I'm not in any of Sam's classes this semester... :(
A Gabi: Yeah, sorry to hear that. But at least you've got it better than me. No one can even come close to understanding what I've been through (ect.) ...
Guy 2: wow, you're so lucky