thumbs down

Short definition from Wiktionary

Noun

1. 1
   A gesture signifying disapproval; a thumb pointing down out of a fist.
2. 2
   A rejection or refusal.
3. 3
   Alternative form of thumbs down.

Verb

1. 1
   third-person singular simple present indicative of thumb down
2. 2
   To disapprove with a thumbs-down sign.