Laugh at idiot returning sponge (6)
I believe the answer is:
loofah
'sponge' is the definition.
(loofah is a type of sponge)
'laugh at idiot returning' is the wordplay.
'laugh' becomes 'ha'.
'at' means one lot of letters go next to another.
'idiot' becomes 'fool' (both can mean a stupid person).
'returning' is a reversal indicator.
'ha'+'fool'='hafool'
'hafool' back-to-front is 'LOOFAH'.
(Other definitions for loofah that I've seen before include "Bath scrubber" , "Dry sponge used for scrubbing" , "Bathroom sponge for washing back" , "Bathroom scrubber" , "Dishcloth gourd" .)