Garment extremely ineffective on naked men (7)
I believe the answer is:
nightie
'garment' is the definition.
(I've seen this before)
'extremely ineffective on naked men' is the wordplay.
'extremely' suggests removing the centre (only the extremes of the word are used).
'ineffective' becomes 'idle' (associated in meaning).
'on' is a charade indicator (letters next to each other).
'naked men' becomes 'night' (I can't explain this - if you can you should give a lot more credence to this answer).
'idle' with its centre removed is 'ie'.
'ie' after 'night' is 'NIGHTIE'.
Can you help me to learn more?
(Other definitions for nightie that I've seen before include "Late shift perhaps" , "Light sleeping gown" , "Clothing worn in bed" , "Loose garment" , "Sleepwear" .)