The most common and most likely answer to this crossword clue is the 15 letter word SELF-IMPORTANCE
I've seen this crossword clue in The Times
S
E
L
F
-
I
M
P
O
R
T
A
N
C
E
Buddy explains!
The straight part
We know that "standing proud" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case standing proud = self-importance.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 SELF-IMPORTANCE mean?
SELF-IMPORTANCE noun- An exaggerated estimate of one's own importance or merit, especially as manifested by the conduct or manners; self-conceit.