How to scold Milo for having an accident in a spot he knew I'd see?

This AM, he went outside and came back in; he then sat on my bed chewing paper and trying to get the phone wire. When I got up, I saw he had pooped in center of floor where door opens. (I’d either see it or slip.)

He had food and water set up properly, but the litter box was a little fuller than usual. He gets cranky also when the bottom of bowl is visible, even tho there is food around edges. How long do I wait for make-up making-out?