A sore loser who happens to also be racist and have a brain no larger than a peanut. They also have exceptionally large mouths and an utter inability to understand basic facts.
This term is usually employed to those people who possess the aforementioned characteristics who actually believe that president Barack Obama, a half-black Hawaiian, was born in Kenya. They also have the delusion that President Obama won't release his birth certificate to the public, despite the fact that no other president has actually been asked to and he actually has it posted, like, all over the internet. Since a fundamental quality of a birther is that he or she cannot understand basic facts, they reject the fact that it exists and go on, contented, that he is spending millions to hide it.
Does that guy really reject this proposition despite the overwhelming evidence that it is true? What a birther!