Deny scarf's misplaced in party costume? (5,5)
I believe the answer is:
fancy dress
'party costume?' is the definition.
(I've seen this before)
'deny scarf's misplaced' is the wordplay.
'misplaced' indicates an anagram.
'deny'+'scarfs'='denyscarfs'
'denyscarfs' with letters rearranged gives 'FANCY DRESS'.
'in' acts as a link.
(Other definitions for fancy dress that I've seen before include "Party costume" , "Themed party attire" , "Frivolous party garb" , "Masquerade costume?" .)