Charlie in holiday footwear? That's a disgrace (7)
I believe the answer is:
'a disgrace' is the definition.
(I've seen this before)
'charlie in holiday footwear?' is the wordplay.
'charlie' becomes 'c' (phonetic alphabet: alpha, bravo, charlie etc.).
'in' means one lot of letters goes inside another.
'holiday footwear?' becomes 'sandal' (sandals may be worn on holiday).
'c' inserted into 'sandal' is 'SCANDAL'.
'that's' acts as a link.
(Other definitions for scandal that I've seen before include "Public disgrace", "Outraging event", "It injures reputation", "Event causing public outrage", "dirt".)