Scoundrel’s magic word to remove a piece of underwear — twice! (3)
I believe the answer is:
cad
'scoundrel's' is the definition.
(cad is a kind of scoundrel)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for cad that I've seen before include "Dishonourable man of decadent sort" , "Blackguard" , "A knave, real rotter" , "A rotter, by Jove" , "One behaves dishonourably" .)