What does "let sleeping dogs lie" mean — and why is it funny?

informal

Meaning

To avoid disturbing a situation that is currently calm, in case you cause fresh trouble.

Where it comes from

An old proverb. The warning is plain — wake a sleeping dog and you may be bitten.

Why it is funny

The gentle humor is how literal the advice still is. A piece of careful, grown-up wisdom about avoiding conflict turns out to be, simply, do not poke the dog.

Used in a sentence

"He's finally stopped complaining, so let's let sleeping dogs lie."