This is the funniest true story I've heard in a while. A friend's refrigerator died the other day, and after it was repaired, she found this thin layer of black dust on everything in the kitchen. She mentioned this to her husband, wondering where it came from.
"Oh, I know what that is," he said. "But you have to promise not to get mad at me."
"Well, when the refrigerator stopped working, I thought maybe the coils needed to be cleaned, so I figured I'd blow some air on them."
She nodded. "One of those cans of air we keep next to the computer?"
"No," he said. "I brought in my leaf blower."