Definition of scummed:
(n) :
(derogatory, slang) A reprehensible person or persons.
(n) :
(uncountable) A layer of impurities that accumulates at the surface of a liquid (especially molten metal or water).
(n) :
(uncountable) A greenish water vegetation (such as algae), usually found floating on the surface of ponds
(n) :
The topmost liquid layer of a cesspool or septic tank.
(n) :
(uncountable, slang, chiefly US) Semen.
(v) :
To remove the layer of scum from (a liquid etc.).