My A-level chemistry teacher liked to paint it onto door frames and in the hallways. Apparently one day he'd left some out in his lab in preparation for this prank, then the school had a surprise inspection. He had to teach his class in front of the inspectors while being constantly interrupted by small purple explosions.

He also liked to let off expired fire extinguishers at his sixth formers out of his window, and he once attempted to use them to propel a pupil sitting on a wheely office chair. Very memorable teacher!