A misanthropist is, basically, a person who dislikes people in general. It is an antonym for a "philanthropist," who cares deeply about others.
The most well-known example of a misanthropist in literature is possibly Moliere's main character, Alceste, in the play The Misanthrope. Alceste is so committed to his own integrity and his own value system that he is completely unable to compromise. This inability exends even to his love interest, Celimene, whom he criticizes harshly for her perceived hypocrisy.
Indeed, Alceste regards most of his fellow citizens and deceitful or hypocritical in some way. He is even critical of the older woman, Arsinoe, who has nothing but admiration for him in turn.
Ultimately, Alceste's inability to compromise or give others any benefit of the doubt causes him to lose any hope of love or a life within a human community. His misanthropy has driven him not only away from his love, but also from human contact in general, and ultimately into lonely misery.
This can be related to life in general as well. The play appears to offer a subtle warning, that personal integrity does not mean much if it cannot accommodate the opinions and needs of others. In short, misanthropy tends to lead to loneliness and misery.