Ladies do climax when holding nylon skirts! (3,5)
I believe the answer is:
hen night
'ladies do' is the definition.
(party or 'do' attended only by women)
'climax when holding nylon skirts' is the wordplay.
'climax' becomes 'height' (both can mean the peak of something).
'when holding' indicates putting letters inside.
'skirts' says to hollow out the word (remove centre letters) (retain the edges).
'nylon' with its centre removed is 'nn'.
'height' enclosing 'nn' is 'HEN NIGHT'.
(Other definitions for hen night that I've seen before include "Amusing the girls, bash" , "Party for women only" , "then may the ladies rejoice" , "Pre-wedding celebration for ladies only" , "Bridal celebration" .)