What does "a busman's holiday" mean — and why is it funny?

informal, British

Meaning

Time off that you spend doing the same thing you do at work anyway.

Where it comes from

A British phrase from the 1800s. The image is of a bus driver spending his day off riding along on a bus.

Why it is funny

The humor is the gentle absurdity of the choice. Free at last, the busman climbs aboard a bus — and the phrase quietly laughs at all of us who cannot quite escape our own jobs.

Used in a sentence

"A chef cooking a huge dinner on her day off is a real busman's holiday."