The most common and most likely answer to this crossword clue is the 5 letter word UH-UH
I've seen this crossword clue in Financial Times
U
H
-
U
H
Buddy explains!
The straight part
We know that "a negative response" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case a negative response = uh-uh.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does UH-UH mean?
UH-UH interjection- No