There are always gonna be those people in the world who care about nothing but themselves. They will ignore you until you have something they want. They will cancel plans if something better comes along. Most importantly though, they will make you believe that its YOUR fault when you say something about it and an argument comes up.
I've dealt with this a lot, and I can't say that I haven't been that person, but it is absurd to treat people like that. It is not necessary to have everything I have or want. I love when these people talk about how awful their friends are, because its so funny that they've picked someone who's JUST like them to be their BFF.
They can't do anything in life without it benefitting them. They will seriously find SOME reason to make a trip to the freaking animal shelter beneficial to them. It. Makes. Me. Sick.