This term can mean many things in my opinion:
1.) They are only around during the "good times", but not there for you, during the bad
2.) The friendship is based on their terms only. Ex. When they call you, you are expected to go out, but when you call them, they do not offer the same courtesy.
3.) They always borrow money, but never lend it
I just think that friendship isn't a one way street. . .