Narcissism is a type of personality disorder. Narcissists not only have a high opinion of themselves, but they have an obsessive need to have other people affirm this superiority, and as a result they engage in a lot of attention-seeking behavior.
Solipsism is a legitimate philosophical position...just not a very
popular one. Much like people don't want to admit universal
skepticism—the idea that no knowledge of any kind is possible—no one
wants to say that he is the only real person in the universe. So it
usually regarded as a dead-end that means you have made a mistake
somewhere if your argument leads to solipsism.
Nevertheless, solipsism as such says nothing about how you will
behave or treat other people. Even if you regard all other people as
some sort of illusion or creation of your own mind, you might treat them
very nicely. After all, you observe that being nice to these phantoms
tends to bring about good results for you. (That is just an example;
it's not to say that egoism—the belief that the good is what benefits
oneself—must be a consequence of solipsism.)