The most common and most likely answer to this crossword clue is the 2 plus 3 plus 2 plus 1 plus 6 letter word AS MAD AS A HATTER
I've seen this crossword clue in The Daily Telegraph
A
S
M
A
D
A
S
A
H
A
T
T
E
R
More clues leading to the result AS MAD AS A HATTER
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.