finger-wag

To move the index finger horizontally back and forth, as to say no or reject something.

To move the index finger repeatedly up and down, as to threaten or reprimand someone.

For these and other reasons, I disagree with reecent critiques of the film, such as Matt Novak's finger-wagging thinkpiece, "Idiocracy Is a Cruel Movie and You Should Be Ashamed for Liking It." (2014)

The movement of the index finger horizontally back and forth, as to say no or reject something.

The movement of the index finger repeatedly up and down, as to threaten or reprimand someone.