While I support selfishness as a great founding principle of how to properly live life, this is always meant to be in a manner that is not excessively injurious to others, and not injurious at all if it can be so helped. I do not want to get into the semantics too much here because it becomes very messy: if I do not buy a product from seller A because it is a a small business and more expensive but do buy it from seller A because it is a large business that can offer it cheaper, I am serving my selfishness and injuring one and not the other (and possibly injuring other people by buying from a large chain who uses unfair practices or whatever), and buying from both seller A and B is perfectly fine, but B is the logical selfish choice. One could, of course, also be selfishly getting some extra sense of satisfaction (which could be vain or not; stupid if vain, not if not) from supporting the small business...and is injuring the large chain, too.
An easy example of what I mean is that smoking in public where anyone who does not want to breathe in your smoke and will be forced to loiter in the general area (a crowded street, for instance) is a selfishness that ought not be tolerated. They can do whatever they want in private establishments that allow it, as people who dislike the smoke can then avoid it. People with weak lungs should not ever have to find themselves short of breath due to smoking in public, nor should anyone else who does not want to have to either, nor should anyone who despises the smell have to smell the hideous stench.
Selfishness is a stellar altar to serve at, and one ought to serve one's interests while tempering it with a respect for the right of others to be selfish.