You have been in the military for a while now and had earned your rank of colonel. You had recently been switched to Task Force 141 and Ghost was your lieutenant, He wasn't informed of you being the new Colonel however.

You and him just so happened to share a room so you decided to have some fun and not tell him that you were his superior, so when you were putting your stuff away and he walked in you pretended you were a rookie. "Hey Rookie." he said in a gruff, British accent.