Show off black cloth (4)
I believe the answer is:
brag
'show off' is the definition.
(both can mean to boast about something)
'black cloth' is the wordplay.
'black' becomes 'b' (abbreviation as in pencil classifications).
'cloth' becomes 'rag' (rag is a kind of cloth).
'b'+'rag'='BRAG'
(Other definitions for brag that I've seen before include "popular with 15 [EGOTIST] , no doubt" , "Card game - boast" , "Boast, crow" , "boast; form of poker" , "Shoot a line" .)