Just as two children come in to look for their forgotten lunch boxes (we hold our program in the cafeteria), and without my having seen them, I got up and announced, "Instantaneous Dance Party!" and spun around flailing my arms and legs, dancing to an imaginary funky beat. For two seconds, then abruptly stopped, stood still and serious, and resumed sitting.
I then noticed the kids standing there bewildered, and upon their departure I proceeded to laugh for like 5 billion hours. My coworkers also found this at least slightly amusing, although perhaps not nearly as much as I did.