Rob a fool? (3)
I believe the answer is:
I believe this is a double definition.
'rob' is the first definition.
'a fool?' is the second definition.
('mug' can be a synonym of 'fool')
(Other definitions for mug that I've seen before include "Gullible person" , "Drinking vessel; rob" , "person's face" , "Tankard" , "simpleton" .)