take down a notch

take (one) down a notch (or two)

To reduce or damage one's ego or pride; to humble or humiliate one. I'm really glad that pompous oaf lost his court case—maybe that will take him down a notch or two. It's about time that someone took Sarah down a notch. Her arrogance is simply intolerable!
See also: down, notch, take
Farlex Dictionary of Idioms.

take down a notch

Also, take down a peg. Deflate or humble someone, as in He's so arrogant that I wish someone would take him down a notch, or That defeat took them down a peg. Both notch and peg in this idiom allude to a series, the former of indentations, the latter of knobs, used to raise or lower something. Specifically, peg alludes to the pegs used to lower a ship's colors. Their figurative use dates from the second half of the 1600s. Also see cut down, def. 4.
See also: down, notch, take
The American Heritage® Dictionary of Idioms by Christine Ammer.
See also:
  • take (one) down a notch (or two)
  • take (one) down a peg (or two)
  • take down a peg
  • take someone down a peg or two
  • bring (one) down a peg (or two)
  • bring/take somebody down a peg
  • knock (one) down a notch (or two)
  • knock (one) down a peg (or two)
  • take the starch out of (one)
  • take the starch out of someone