The most common and most likely answer to this crossword clue is the 5 letter word HUMPH
I've seen this crossword clue in The Daily Telegraph
H
U
M
P
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 HUMPH mean?
HUMPH verb- To utter "humph!" in doubt or disapproval.
- Used to express doubt or disapproval