Selfish people get on my nerves =/ I tend to just ignore them and stay away from them, but sometimes I do get into arguments with my step dad who is a REALLY selfish man. Doesn't always end well, lol, so I'd suggest keeping your distance if you can't make a point to them. And yes, be confident! If you show them that you don't care, and that their attitude and opinions mean NOTHING to you, then you're better than they are and they will eventually leave you alone. Other people will realize their appalling behavior and stay away as well. I have had my clashes with many selfish people =P (not clashes as in fight, but I have encountered many)
If the selfish person is close to you, or you can't entirely escape them, when they insist you give them something or agree with them about something, tell them in a strong voice that you will not give them your things or what they want. It will eventually slow them down. For example: in school they may want your pencil or paper. You say "No! These are mine. You should have brought your own." At work if they want you to do their work, or buy them lunch, again you insist they must do their work or buy their own lunch, etc. Don't be afraid you are not being,"nice." Selfish people will continue to take advantage of you as long as you let them. The person you have to be nice to is yourself.
We don't need selfish people in our lives.Life is complicated enough and we don't need people who make it even more difficult for us.Do not be afraid to let them go and seek new friends.It sounds hard and difficult but it's the only way and we always bounce back NO MATTER WHAT.If you are surrounded by selfish loved ones then the only thing you can do is to just distance yourself from them but not cut them off completely.You can also try to talk with some that mean a lot to you,let them know in a very polite way how you feel and how their behavior is troubling you.