Reject song meaning
There are two legends about this song. One is that the band All-American Rejects got its name from the line in this song. And the other one is that the song is about a woman who sent a letter to Green Day saying that their music is worthless and what they do is garbage. Both the woman's letter and the response to it are available on the net, but it is unknown whether either of them is real or just made up by some fan-site to back up the legend.
The song has interesting lyrics. The narrator says that criticism doesn't bother him since he's doing what he wants and even if that would make him a reject it is still the road he chooses to walk and he's proud of it. But what is more interesting is that the song describes a certain type of people - those who consider themselves good enough to tell others what to do. They are irritated by people who they believe to be worthless and want them to change their ways and become more like the norm. The narrator tells those know-it-alls to stop flattering themselves because they are not perfect either and their desire to make everyone fit their ideal social model will only screw them up and turn them to "nervous wrecks". In other words, it's much better to be a reject but do what you want than always follow patterns and do what you are told just for the sake of being accepted by society.