My group tends to use either the term Neckbeard, or, Elite Veteran Gamer. Though that might be a little more specific form of pomposity than fatbeard. You know somebody's a fatbeard when they bring their game playing experience into a discussion that has nothing to do with it. As in "As an elite veteran Gamer whose GMed for 31 years, I disagree, even though my opinion isn't based in logic, fact, or even concept." That might be more of a message board thing, but it's kind of the same problem in gaming.
Anyway, the problem with using a term like fatbeard playfully to let your friends know they're being douches is that it's just the next step on the euphemism treadmill. People probably used to use munchkin playfully before it became a gamer curseword.