Idiot in loafers (3)
I believe the answer is:
oaf
'idiot' is the definition.
(I've seen this before)
'in loafers' is the wordplay.
'in' says the answer is hidden in the clue.
'OAF' is hidden within 'loafers'.
(Other definitions for oaf that I've seen before include "one of thick character" , "A clumsy boor" , "Boor or lout" , "Stupid or loutish person" , "Lout, dullard" .)