Expose girl coming out to meet headless macho man (6)
I believe the answer is:
debunk
'expose' is the definition.
(to debunk is to expose as false)
'girl coming out to meet headless macho man' is the wordplay.
'girl coming out' becomes 'deb' (short for debutante).
'to meet' says to put letters next to each other.
'headless' means to remove the first letter.
'macho man' becomes 'hunk' (a hunk is a muscular man).
'hunk' with its first letter removed is 'unk'.
'deb'+'unk'='DEBUNK'
(Other definitions for debunk that I've seen before include "Show to be exaggerated or false, claim or theory" , "Disprove" , "Reveal as false, show up" , "Expose pretensions of" , "Show to be falsely honoured" .)