Airsoft pellets all over the basement floor.
Cleaning up videogame controllers in the morning, coming back down in the afternoon and cleaning up the same controllers, even though I KNOW FOR A FACT that they did not play that game. They just took the controllers out and spread them on the floor. And removed a lot of the batteries, while they were at it.
Being told that it is His Right to have a messy room. And having to explain that His Right to a messy room extends only so far: not, for instance, to the point where we are ALL enjoying roaches.
Washing folded laundry: because if you leave clean laundry on the floor long enough, the dog will pee on it.
Knowing that I have a family history of children who never leave The Nest. Please, God, make them want to get the hell out when they graduate.