What does "pull someone's leg" mean — and why is it funny?

informal

Meaning

To tease or fool someone in a playful, harmless way; to tell them something untrue as a joke.

Where it comes from

Uncertain. It appears in the 1800s, and the various grim 'explanations' offered for it are themselves mostly leg-pulls.

Why it is funny

The humor is the gap between the gentle meaning and the slightly odd action. Teasing a friend has nothing to do with their leg, yet the phrase picks that one specific limb and tugs — and fittingly, even its own origin story is probably a joke.

Used in a sentence

"Relax, I didn't really sell your car — I'm just pulling your leg."