definition matters

[elena]

Just a curious fact: within 2 weeks, I have spotted 3 instances of "bottom
feeder" in different places (lbo, wojtek's; dc, don't_remember _who; another
list); what does it mean?
The Cassel Dictionary of Slang gives the following alternatives:
bottom feeder n. [1970's] (US teen)
1. a despicable, unpleasant person
2. one who has yet to make their mark, a 'wannabe'
3. a social outcast
4. a gossip, esp. a trader in malevolent and harmful stories
[SE bottom feeder, a fish that feeds off the sea- or riverbed]

What other social types are there, in terms of feeding/food? Any equivalent
for parenteral feeding? Or as prescribed by religion (brain-fasters or
smth)?

(not a troll - a REAL question; off-list OK)