The best prank I know of was actually done by university students.
It was April 1st, the brittish equivalent of Roish Choidesh Adar, and soem students found out that the municipitality was planning on doing some road repairs outside their school.
The students approached the police and informed that some students were planning an April’s fools plank, and they were going to pretend that they were maitenance workers digging up the road. The same studants then approached the workers, and let them know that somes tudents dressed up as Police would try and disrupt the roadworks on the next day. The students went the next day and watched how the real police argued with the real road workers, each side fimly convinced that they were talking to students.