Years ago I heard an elder family member refer to Scandinavia as "Squareheddy." When I asked, I was told, "because that's where the Squareheads come from." I didn't know it was also used of Germans. I guess it could be pinned on a large portion of humanity, though.

"Frogs," "frog-eaters," or alliteratively "frog-eating French": the initial "fr" is probably why frogs rather than snails were chosen for this piece of disparagement.