One's out of time, wearing most unlikely current fashion (6)
I believe the answer is:
latest
'current fashion' is the definition.
'one's out of time wearing most unlikely' is the wordplay.
'one's' becomes 'im' ('one is' is a formal way of saying 'I am').
'out of' is a deletion indicator.
'wearing' is an insertion indicator.
'most unlikely' becomes 'last' (I've seen this before).
'time' with 'im' taken out is 'te'.
'te' placed into 'last' is 'LATEST'.
(Other definitions for latest that I've seen before include "Most recent or most unpunctual" , "Most recent or most tardy" , "coming after all the others" , "Most recent, hot off the press" , "style of today" .)