The most common and most likely answer to this crossword clue is the 8 letter word BRAGGART
I've seen this crossword clue in Financial Times
B
R
A
G
G
A
R
T
More clues leading to the result BRAGGART
- A person who boasts about good fashion knowledge
- Boastful chap in card game having good skill
- Dress up with band, not Queen, one boasts
- I boast highbrow subject introduced by appropriate presenter
- Swank — crazy rag bag, right?
- Humphrey is making ordinary jazz style one to show off
- Show-off‘s end of short cloth dress reflected
Buddy explains!

The straight part
We know that "Boastful chap" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case boastful chap = braggart.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 BRAGGART mean?
BRAGGART noun- Someone who constantly brags or boasts.
- Characterized by boasting; boastful.