One contributer to MyOldHouseOnline.com finds humor in things you can learn from a McMansion:

1) The builders did not have all the answers.  Sometimes, they didn’t understand any of the questions.  Feel free to display bewilderment and dismay at their cluelessness.

2)  When you find a light or window in an inexplicable location or missing where one should decidedly be, refer to lesson #1.

3) Four words: What Were They Thinking?

4) McMansion owners can be the best-dressed people at the party.  But when the party is at their house, try not to stare, point, or snicker…

The main joke here appears to be that McMansions are not built that well. Hence, be prepared to find lots of things to fix or to have to make major changes to poor decisions by builders.