An eating disorder
Joke:What is a joke?
A man walks into the Doctors with an apple in one ear, a banana in the other ear and grapes up his nose. He says, "Doctor, what's happening to me?" The doctor replies, "You're not eating properly.
Normally, "you're not eating properly means, "you're eating the wrong things." Here though, it means, literally, you're not eating in the normal way, ie with your mouth.