finger-wag

Short definition from Wiktionary

Verb

1. 1
   To move the index finger horizontally back and forth, as to say no or reject something.
2. 2
   To move the index finger repeatedly up and down, as to threaten or reprimand someone.

Noun

1. 1
   The movement of the index finger horizontally back and forth, as to say no or reject something.
2. 2
   The movement of the index finger repeatedly up and down, as to threaten or reprimand someone.