What does "a whippersnapper" mean — and why is it funny?

informal, humorous, dated

Meaning

A young person who is overconfident, cheeky, or presumptuous — usually said by someone older.

Where it comes from

An English phrase from the 1600s, probably from 'snippersnapper' or the idea of an idle youth snapping a whip about with nothing better to do.

Why it is funny

The humor is how the word itself sounds like a telling-off. It snaps and cracks as you say it, and it carries the unmistakable tone of an exasperated grandparent — a whole grumpy mood folded into one word.

Used in a sentence

"Some whippersnapper told me I was using the computer wrong."