I enjoy this page of Milne's Tips for Authors.
I also find the book Mathematics Made Difficult by Linderholm to be hilarious. I'm not going to search for favorites, but I find the first 2 exercises amusing:
"1. Show that a finite subset of an arbitrary set E in a ring suffices to generate the ideal generated by E if, and only if, the ring is Noetherian.
*2. Show that 17 x 17 = 289. Generalize this result."
