Joey has picked up a new phrase.
Even though the enunciation is lacking, the tone and volume are unmistakable. He's obviously heard it many times from Sir-Poops-a-Lot himself, Big Brother Micah -- who has made up a song (sung very loudly) to let us know that he is in need of some hiney-wiping assistance.
It's just hilarious to hear Joey singing, from his carseat, from his bed, in the middle of the living room, "I'm finished! I'm fi-i-i-i-nished!" :)