What does "chew the fat" mean — and why is it funny?

informal

Meaning

To chat in a long, relaxed, friendly way about nothing in particular.

Where it comes from

Uncertain. One idea links it to sailors or farmers passing time while literally chewing tough salted fat, though it is the comparison to idle talk that stuck.

Why it is funny

The humor is how unappetising the image is for something so pleasant. A warm catch-up with a friend gets described as gnawing endlessly on a lump of fat — slow, chewy, and going nowhere, which is oddly fitting for aimless conversation.

Used in a sentence

"We sat on the porch and chewed the fat until it got dark."