My cats don't have any problems as far as litterbox etiquette, but Skeletor had the most godawful death breath for a while because of the flea collar I had on him. Don't ask me how, but that's what caused it. What made it worse was the fact that he likes to perch on my shoulder while I'm on the comp, and every so often he'd crane his neck around so that he was right in my face. And then he'd yawn. Nine times out of ten I dry-heaved.
Of course, there was the time he gassed me away from the computer. He was just sitting on top of the monitor all sweet-like, then daintily jumped to the floor to saunter off. Two seconds later I found out why. You know it's bad when even the culprit can't stand his own dirty deeds.