The most common and most likely answer to this crossword clue is the 7 plus 6 letter word UTTERLY STUPID
U
T
T
E
R
L
Y
S
T
U
P
I
D
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.