The most common and most likely answer to this crossword clue is the 6 letter word LOUDER
I've seen this crossword clue in The Guardian
L
O
U
D
E
R
Buddy explains!

The straight part
We know that "More flamboyant" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case more flamboyant = louder.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 LOUDER mean?
LOUDER adjective- (of a sound) Of great intensity.
- (of a person, thing, event, etc.) Noisy.
- (of a person, event, etc.) Not subtle or reserved, brash.
- (of clothing, decorations, etc.) Having unpleasantly and tastelessly contrasting colours or patterns; gaudy.
- (of marijuana) High-quality; premium; (by extension) having a strong or pungent odour indicating good quality