Dressing down? Theatregoers are beneath it (7)
I believe the answer is:
reproof
'dressing down?' is the definition.
(both can mean criticism)
I can't explain the rest of the clue.
(Other definitions for reproof that I've seen before include "work on raincoat?" , "Dressing down" , "Once more get water-resistant" , "Reprimand" , "what mac no longer keeping one dry needs?" .)