Littlest complaint, in an idiom (3)

I believe the answer is:

boo

(Other definitions for boo that I've seen before include "Make one's dislike heard" , "Frightening word (for a goose?)" , "Express noisy disapproval" , "Disapproving sound" , "Exclamation of disapproval" .)

I've seen this clue in The New York Times.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.