Fail to show up a hairdresser? (4,1,7)
I believe the answer is:
come a cropper
'fail' is the definition.
(I've seen this in another clue)
'show up a hairdresser?' is the wordplay.
'show up' becomes 'come' (I've seen this in another clue).
'hairdresser?' becomes 'cropper' (someone who crops hair).
'come'+'a'+'cropper'='COME A CROPPER'
'to' acts as a link.
(Other definitions for come a cropper that I've seen before include "Fall heavily and unexpectedly" , "Suffer a defeat" , "Fail spectacularly" , "Fail badly" .)