Never Catch a Falling Knife
There's a character in Douglas Adams' "So Long and Thanks for All the Fish" who is driven mad by operating instructions on a box of toothpicks.
I think stuff like that is great. My college roommates and I had the Wall of Wack at our house. The wall was devoted entirely to excessive warning labels, funny pictures, a "Shoplifters will be prosecuted sign" that we stole. It was funny then. Guess you had to be there.
Here's a site and contest devoted to funny warning labels, including the winner, a heat gun that warns "Do not use as a hairdryer." Rad.