Unless you’re left-handed and your left foot is dominant – then being ambidextrous would be like having two left hands, and being klutzy would be like having two right feet.
I like the pun, but a self-insert doesn’t automatically equal Mary Sue/Gary Stu (just like an OC and/or a character whom someone doesn’t like =/= Mary Sue/Gary Stu).
Its origin aside, I have a feeling that the reason why this riddle appears in this strip is because it was mentioned in The Last Unicorn (both the book and the movie).
Unless you’re left-handed and your left foot is dominant – then being ambidextrous would be like having two left hands, and being klutzy would be like having two right feet.