One of the best pranks I've ever witnessed was pulled on a class I was teaching, about a dozen years ago. As was customary then the senior year students went on a week long foreign trip accompanied by a couple of teachers. That year, it was a survival week in the hills of the Ardennes (Belgium).
First night we organized a night dropping. The students had to find their way back to the camping site in the dark, using flashlights, compasses and a detailed map. The teachers (I was one of them) went along with them, just in case.
At one point, the group had to cross a creek. As we were wading through the (cold!) water, one of the girls started screaming and pointed at something in the water.
A shark dorsal fin, moving towards us. A fairly big one too.

Of course, it was a scuba diver who had strapped a fake dorsal fin to his back. But none of the students realised that sharks don't live in freshwater creeks...

I almost busted my gut laughing.

The pen is mightier than the sword. But if you literally want to have some impact, use a typewriter

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