A nationalist according to me is a person blinded by his admiration for his own country, and there for not able to clearly perceive the rest of the world.
Nationalism is IMO more often an obstacle than the opposite for many people to cooperate with other people and seeing them as having an equal right to exist.
Nationalism is based on the same feelings and mechanisms in the human animal as racism, and is equally bad.
But one should not equal Nationalism with Patriotism, unfortunately a lot of people call them selfs patriots when they actually are nationalists.
My definition of patriotism is finding your home land good, and as good as any other country.
Whilst Nationalism is all about believing that your nation is better than all other countries, which is a very unhealthy attitude because of the importance of cooperating with other nations for the sake of your own nation.
For example a lot of Americans call themselves patriots, but think of the USA as the best country in the world. This makes them nationalists IMO, and is quite sad and sickening to watch.