Sorry folks-I hit some button or something and posted before I finished. Here is my actual reply:
There is so much humor in Mahler, of all sorts--genuinely funny, grotesque, witty, you name it. Let me point to just two very small examples that had me laughing out loud and that, all questions of subjectivity aside, I think most people will hear and agree with.
1. The final bars of the First Symphony's first movement, there the timpani get so carried away that they pound along solo until stopping dead, as if embarrassed. Then they and the rest of the orchestra can't seem to get in sync with one another, before finally, after two attempts, they finally manage to finish at the same time. That, to me, is genuinely funny.
2. The last bar of the Ninth's first scherzo--piccolo and contrabasson, and nothing in the middle. This is almost exactly the same sound that Verdi used in Falstaff's monolog in which he considers with horror the prospect of starving and becoming thin.
The problem with humor in music is twofold: it depends on timing above all else, and we are so conditioned to take the music seriously that we don't LET ourselves laugh, and take the music that makes us want to laugh at face value. We feel there must be something wrong with us. I remember very vividly that I was once on a date in high school with a girl who had never been to a symphony concert. We were listening to the second movement of Tchaikovsky's Pathetique Symphony (not exactly a laugh riot of a piece, let's face it). At one point, the main them comes in accompanied by running pizzicatos in the violins, and she started laughing. She simply found the sound deliciously witty. And it was, but I, who knew it very well, had to think about it and say to myself, "Wait a minute. Maybe it really IS as witty as it sounds and familiarity has bread a certain degree of contempt." The lesson is to try to keep the experience of listening fresh and have the confidence to let yourself feel spontaneously, because if humor isn't spontaneous then it certainly isn't funny.
Dave H