Crowning moment, capturing a couple of Poles in celebration (3,5)
I believe the answer is:
hen night
'celebration' is the definition.
(I know that hen night is a type of bachelor(ette) parties)
'crowning moment capturing a couple of poles in' is the wordplay.
'a couple of poles' can mean two replacements for 'pole'.
'crowning moment' becomes 'height' (I've seen this before).
'capturing' indicates putting letters inside.
'pole' becomes 'n' (abbreviation for North, as in North Pole).
'pole' becomes 'n' (abbreviation for North, as in North Pole).
'in' is an insertion indicator.
'height' going around 'n' is 'henight'.
'henight' enclosing 'n' is 'HEN NIGHT'.
(Other definitions for hen night that I've seen before include "Bridal celebration" , "party of girls" , "prematch party" , "Bride's celebration before wedding" , "Party for women only" .)