April Fool's Day: What's the best prank you've ever done?

Tell us whats the Best Prank you've ever done, or you ever gotten? :D

Ima tell you mine.

It happened 2 years ago, the seniors was having their Mock IGCSE exam (Cambridge Syllabus)

almost everybody ganged up on one of my friend said that they change the exam schedule, which means on that day it was other subject exam. Of Course she was freaking out, i died the whole entire week laughing about it. Well i wasn't the only one, but still.

What's yours :) sharing is caring :P