The most common and most likely answer to this crossword clue is the 3 letter word UGH
I've seen this crossword clue in Financial Times
U
G
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 UGH mean?
UGH interjection- Used to express repugnance, disgust, or annoyance.
- Used to express inarticulate vocalisations, such as used by a caveman.