Interestingly enough, it's my 13-year old cat Stump who does this to me, usually when I first get up in the morning and am heading for the shower. He'll walk behind me and then grab the back of my leg with his front paws; sometimes he'll even give me a little play bite. He had stopped doing this for awhile and then started it up again fairly recently. I respond by calling him Silly Stump, and then he always responds by rolling over onto his side and rubbing his head on the carpet. This is sometimes followed by "Flippy Cat," which is when he lies on the floor and flips from one side to the other.

Emmett's "RCOs" are only directed at Stump!