"Why does your geography exam have a big zero over it."
"It's not a zero, the teacher ran out of stars, so she gave me a moon instead!"
When NASA first started sending up astronauts, they quickly discovered that ballpoint pens would not work in zero gravity. To combat the problem, NASA scientists spent a decade and $12 billion to develop a pen that writes in zero gravity, upside down, underwater, on almost any surface including glass and at temperatures ranging from below freezing to 300 C.
An Air Force cargo plane was preparing for departure from Thule Air Base in Greenland. They were waiting for the truck to arrive to pump out the aircraft's sewage holding tank. The Aircraft Commander was in a hurry, the truck was late in arriving, and the Airman performing the job was extremely slow in getting the tank pumped out.
When the commander berated the Airman for his slowness and promised punishment, the Airman responded: "Sir, I have no stripes, it is 20 below zero, I'm stationed in Greenland, and I am pumping sewage out of airplanes. Just what are you going to do to punish me?"