Scoundrel ordered gallon after gallon (3,3)
I believe the answer is:
bad egg
'scoundrel' is the definition.
(both can mean an unpleasant person)
'ordered gallon after gallon' is the wordplay.
'ordered' becomes 'bade' (past tense of 'bid' as in to order).
'gallon' becomes 'g' (abbreviation for the unit of liquid).
'after' says to put letters next to each other.
'gallon' becomes 'g' (abbreviation for the unit of liquid).
'bade'+'g'+'g'='BAD EGG'
(Other definitions for bad egg that I've seen before include "Unpleasant person" , "Worthless individual" , "A rotten ovoid" , "Nasty person like addled ovoid" , "Dishonest person like addled ovoid" .)