Why do some people only speak and come around you when they need something?

United States
January 7, 2010 10:44pm CST
I have encountered some people who only want to speak or come around when they need something, as soon as they doing well i do not hear from them and if i do see them they act is if i don't exist . Why can't some of these people realize they are coming off as phony users . What is the best way to deal with some of these moochers?