The most common and most likely answer to this crossword clue is the 4 plus 4 letter word GLAD RAGS
I've seen this crossword clue in The Times
G
L
A
D
R
A
G
S
More clues leading to the result GLAD RAGS
- Jokes about youth, Republican, in best clothes
- Cross-dressing in something transparent, almost, just the thing for party?
- Good boys protecting kid in best clothes
- . Jokes about youth with rare finery
- Best clothes: those seen on TV, viewed in short mirror
- Top Gear‘s blokeish type appearing in German papers
- The best clothes for happy kids
- Best clothes in tatters after having left to wander around
- Top Gear – jokes involving juvenile humour in the extreme
- Jokes about boy heading for Roedean in best clothes
Buddy explains!

The straight part
We know that "just the thing for party?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case just the thing for party? = glad rags.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.