The most common and most likely answer to this crossword clue is the 9 letter word POSTURING
P
O
S
T
U
R
I
N
G
Buddy explains!

The straight part
We know that "showing off" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case showing off = posturing.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 POSTURING mean?
POSTURING verb- To put one's body into a posture or series of postures, especially hoping that one will be noticed and admired
- To pretend to have an opinion or a conviction
- To place in a particular position or attitude; to pose.
- The assumption of an exaggerated pose or attitude.
- The behaviour of some birds as a means of signalling etc.