The most common and most likely answer to this crossword clue is the 16 letter word SELF-CENTREDNESS
S
E
L
F
-
C
E
N
T
R
E
D
N
E
S
S
Buddy explains!
The straight part
We know that "narcissism" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case narcissism = self-centredness.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.