I was lucky to be there to watch.
One of the most epic pranks one of my brothers did to another was completely improvised and well timed. To make it easier to read let`s call them "Jack" and "Steve".
They were having a pillow fight, and Jack hits Steve so hard that Steve falls to the floor.
When Steve fell off, his ear touched the floor and felt an earthquake comming( we live in a seismic country). He gets up, says he got angry and is time to get serious, screams like a super saiyan and while he is screaming, the quake starts. After witnessing this Jack was so shocked his skin got pale.
(don`t worry, while the quake felt strong it wasnt a dangerous situation because it was pretty short in duration and our house is anti-seismic.)