Here is what is funny - stereotypes assign specific attributes to a large population, generally negative.. They are everywhere for every race, national origin, gender, religion. Perhaps also there is the stereotype that if you find humor in jokes about stereotypes - then you are a bigot. Kind of a Mobius Strip - http://www.math.hmc.edu/~gu/curves_a...s/moebius.html
See how I tied this in to a context relevant comment (Mobius).
Personally I find sterotypical jokes about old white married guys pretty funny - because I can identify with them at a certain level and I can laugh at myself.