Idiot girl removing top (3)
I believe the answer is:
ass
'idiot' is the definition.
(I've seen this before)
'girl removing top' is the wordplay.
'girl' becomes 'cass'.
'removing top' means to remove the first letter (I've seen 'removes top' mean this).
'cass' with its first letter removed is 'ASS'.
(Other definitions for ass that I've seen before include "sap" , "Charlie" , "transporter" , "Silly fellow in passionate state" , "Idiotic animal" .)