How can I subtly avoid a two-faced coworker without giving the impression that i am being sulky?

Do the opposite to sulking. Walk around looking like the cat that got the cream. It drives them barmy because they don't know what you're looking so secretively happy about. It works and it is hilarious watching them nudge each other and whispering. I bet you any money that one of the nosey cows will try and talk to you to find out. LOL Just act nonchalant if they ask and say you have no idea what they mean. I promise you, you will laugh your head off by the end of the day.