bottom feeder
noun /ˈbɒtəm fiːdə(r)/
  /ˈbɑːtəm fiːdər/
- (North American English, informal) a person who earns money by taking advantage of bad things that happen to other people or by using things that other people throw away乘人之危谋利的人;利用他人丢弃物为生的人;拾荒者 
- a fish that feeds at the bottom of a river, lake or the sea底栖鱼