Pineapple class admitting topless men? (7)
I believe the answer is:
grenade
'pineapple' is the definition.
(pineapple can informally mean a grenade)
'class admitting topless men' is the wordplay.
'class' becomes 'grade' (grading is a kind of classing).
'admitting' is an insertion indicator (admit can mean to welcome in or accept).
'topless' means to remove the first letter.
'men' with its initial letter removed is 'en'.
'grade' placed around 'en' is 'GRENADE'.
(Other definitions for grenade that I've seen before include "Bomb with a pin" , "Small hand missile" , "Missile thrown" , "Pineapple" , "Small bomb thrown by hand" .)