Positive, Comparative, Superlative

Been a while since I mentioned this fairly common error (but I have mentioned it. More than once.). 

When you compare two things, use the form that ends in -er: steeper, sweeter, longer.
When you compare three or more, the winner gets the -est form: steepest, sweetest, longest.

That makes it easy to tell what form they should have used in the last panel:


Unless maybe they’re including the rest of the world???