What does "a cock and bull story" mean — and why is it funny?

informal

Meaning

A far-fetched, unbelievable story or excuse.

Where it comes from

An English phrase from the 1600s. Its true source is unknown, with one theory pointing to two old coaching inns, the Cock and the Bull, where tall tales were swapped.

Why it is funny

The humor is the barnyard nonsense of the name. An elaborate lie gets dismissed by invoking, for no clear reason, a rooster and a bull — and the phrase sounds exactly as made-up as the stories it describes.

Used in a sentence

"He gave me some cock and bull story about his car being taken by a circus."