Shane has been like this lately, considering he put Rick on his sights one time in the woods (and if you've read the comic book, you'll understand that he does become sort of spiteful against Rick and his family, he's a little jelly). You see him transform from Rick's caring buddy to this guy who's very envious and mean-spirited. They couldn't have made it both, it was kind of dire. So Shane trying to fend for his own (and being a little evil) decided to buy himself some time by "distracting" the walkers with a feast (Otis).