That's what we call a zinger!

zinger informal noun Yost got us with a few good zingers. Also known as a quip, joke, criticism, dig or poke, zinger (or Zing! for short) is a great word.

Here, for example, is a zinger. This is from a review by Charles McGrath of "My Freshman Year: What a Professor Learned by Becoming a Student," by Rebekah Nathan:

For a layperson, it's hard to understand the fuss, because "My Freshman Year" is a surprisingly bland book, encumbered by a lot of handwringing over niceties of procedure. It says next to nothing, for example, about sex and drinking among college students, which is a little like writing about the Tongan Islanders (Ms. Small's academic specialty) and neglecting to mention that they hunt and gather. [Zing!]