Economists Are a Joke?

A smarty-pants old story says that if you want a "learned economist," all you have to do is get a parrot and train the bird to squawk "supply and demand" in response to every question.

Not fair, but ...

It's true that the "theory of supply and demand" is a central part of economics. It is widely applicable, and also is a model of the way economists try to think most problems through, even when the theory of supply and demand is not applicable.

What is it?