Hee! I have to admit that joke was inspired by a friend's scathing comment about a terrible bottle of wine. He took a mouthful and then said, in a perfect deadpan: "I wonder how they got the cat to piss in the bottle?" I had to steal it for this story! I'm sure he wouldn't mind.
When I reread the scene in DH where the Dursley's are leaving, I was really moved by Dudley's attempt to articulate his feelings about Harry. That was one of the (few) things in the book I actually thought JKR handled perfectly. I would love to read your Dudley fic. I'll look for it once I get caught up on comments!