@The Pentacle Queen,
Humour can be used in otherwise unbearable situations. I read a book called "Mans search for meaning", which describes a psychologists experience of being a prisoner of war in WW2. He found often that among the group that he was with there was a lot of humour, and humour served as a coping mechanism in an intolerable situation.
To be able to make people laugh, however, is a form of power, and thats part of the pleasure in being funny.
Absurdity is a big part of it maybe. When we laugh at someone's seriousness, we do so because we don't find their seriousness feasible in relation to what it is that they are serious about, and so we find it "Absurd", and we laugh.