The most common and most likely answer to this crossword clue is the 8 plus 4 letter word BIRTHDAY SUIT
I've seen this crossword clue in The Guardian
B
I
R
T
H
D
A
Y
S
U
I
T
More clues leading to the result BIRTHDAY SUIT
- Everyone arrives in this type of party clothing
- Nothing actually to wear? I’d buy a T-shirt, possibly
- First-day cover?
- Fashionable bit with dusty hair and skin
- A British duty to arrange garb for streakers?
- Awfully dirty? Bath is useful at outset – in this?
- The raw bananas: I try a dish, but …
- One’s altogether united in disguising dirty habits
- Original outfit barely appropriate for annual celebration?
- Nothing to wear for annual event?
Buddy explains!
The straight part
We know that "Everyone arrives in this/ype of party clothing" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case everyone arrives in this/ype of party clothing = birthday suit.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.