The most common and most likely answer to this crossword clue is the 5 letter word WITTY
I've seen this crossword clue in Independent
W
I
T
T
Y
More clues leading to the result WITTY
Buddy explains!

The straight part
We know that "Sarcastic" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case sarcastic = witty.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 WITTY mean?
WITTY adjective- Wise, having good judgement.
- Possessing a strong intellect or intellectual capacity; intelligent, skilful, ingenious.
- Clever; amusingly ingenious.
- Full of wit.
- Quick of mind; insightful; in possession of wits.