A weird incongruity. Derived from the fact that Goofy and Pluto are both dogs in the world of Disney characters, yet Goofy walks on two legs and talks, while Pluto barks, walks on all fours and is otherwise a non-anthropomorphized dog. Usage as explained by Tina Fey on NBC.com's "Ask Tina" video clip.
First guy: That new girl in accounting is so hot. But what's up with those big floppy clown shoes she's always wearing?
Second guy: Right? That's a Goofy Pluto, alright.