Topless men sing drunkenly for officer (6)
I believe the answer is:
ensign
'for officer' is the definition.
(I've seen this before)
'topless men sing drunkenly' is the wordplay.
'topless' means to remove the first letter.
'drunkenly' indicates anagramming the letters.
'men' with its initial letter taken off is 'en'.
'sing' is an anagram of 'sign'.
'en'+'sign'='ENSIGN'
(Other definitions for ensign that I've seen before include "Flying" , "Commissioned rank in some navies" , "Standard - flag" , "Low-ranking naval officer" , "National flag" .)