Originally an abreviation, or abrev, of the word Feasible. However, it was used almost exclusively by the preppy "that guy" crowd. As Such, Feas has come to represent a lifestyle. Namely That of "That guy" the man who pops his collar for no reason, brags about how much he has drank, and makes loud remarks about his trust fund.
Often used in the Cincinnati Land area
"Dude, quite popin' your collar that's so feas"
"Dude, I was at this party but it was such a feasfest that I had to leave in disgust"