scum

noun
1
a layer of bubbles or an unpleasant substance that forms on the surface of a liquid
کف, پوسته, چرک سطحی, آشغال روی آب, کف آب
2
an offensive word for people who you think are very bad
آدم بی‌ارزش, پست, آدم بد
Don't waste your sympathy on scum like that.
Drug dealers are the scum of the earth.