Mouth-pieces from Down Under may ultimately do for men? (4,5)
I believe the answer is:
stag party
'mouth-pieces from down under may ultimately' is the definition.
I can't judge whether this defines the answer.
'do for men?' is the wordplay.
'do' becomes 'party' (I've seen this before).
'for' means one lot of letters go next to another (I've seen this in other clues).
'men?' becomes 'stag' (I've seen this before).
'party' put after 'stag' is 'STAG-PARTY'.
Can you help me to learn more?
(Other definitions for stag party that I've seen before include "Rowdy celebration for men only - or deer?" , "event for men" , "Boozy celebration for men preceding wedding" , "A drinking night out for groom-to-be, men only" , "Rollicking night out for men" .)