What does "carrying coals to Newcastle" mean — and why is it funny?

informal, British

Meaning

Doing something completely pointless, because you are supplying something to a place that already has plenty of it.

Where it comes from

A British phrase from the 1600s. Newcastle was England's great coal-mining city, so bringing it coal was the very picture of a wasted errand.

Why it is funny

The humor is the proud, sweaty pointlessness of the image. You picture someone hauling a heavy load all the way to the one town on earth that needs it least.

Used in a sentence

"Bringing wine on a tour of the vineyard felt like carrying coals to Newcastle."