The most common and most likely answer to this crossword clue is the 6 letter word KVETCH
I've seen this crossword clue in Financial Times
K
V
E
T
C
H
Buddy explains!

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 KVETCH mean?
KVETCH noun- A person who endlessly whines or complains; a person who finds fault with anything.
- An instance of kvetching; a complaint or whine.
- To whine or complain, often needlessly and incessantly.