The most common and most likely answer to this crossword clue is the 7 plus 4 plus 5 plus 6 letter word DAMNING WITH FAINT PRAISE
I've seen this crossword clue in Financial Times
D
A
M
N
I
N
G
W
I
T
H
F
A
I
N
T
P
R
A
I
S
E
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.