bottom feeder

from The American Heritage® Dictionary of the English Language, 4th Edition

• n. A fish or other animal that feeds on the bottom of a body of water.
• n. One that feeds low on the food chain; a scavenger.
• n. Slang An opportunist who profits from the misfortunes of others: "The frazzled, adrenaline-pumped tabloid newshounds [in the movie] are the bottom feeders of contemporary journalism” ( Entertainment Weekly).
• n. Slang A low or despicable person.

from Wiktionary, Creative Commons Attribution/Share-Alike License

• n. A fish or other aquatic creature who feeds off the bottom of their habitat; a flatfish
• n. A person who dwells amidst or thrives off of the unwholesome things in a society

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• n. an opportunist who profits from the misfortunes of others