Harry and Elsie's exchanges have a tendency to be pretty darn funny. But this one from The Pond Couple, in this troper's opinion, takes the cake (Everything except Harry's line is slightly paraphrased)
Elsie: It may surprise you, but even Harry and I didn't get along when we first met
Stanley: You didn't? How come?
Elsie: Well, Harry's a dog and I'm a cat
Harry: You're a cat? I thought you were a chihuahua
- May very well be a Shout-Out to Animaniacs. Unlikely though