1) Fill a bucket with water.

2) Open a door, and balance the bucket on top.

3) Wait for someone to open the door.

4) Laugh as the bucket of water falls down and smashes the someone's teeth out.

That's a famous prank, known in the pranking trade as 'Bucket, Water, Door, Balance, Fall, Bucket, Teeth', or 'BWDBFBT' (pronounced 'Bawda-bif-a-bot').
BWDBFBT is one of the oldest pranks in existence, first documented by the ancient Greek historian Herodotus: he describes in great detail how he used it on his arch nemesis, Thucydides.

But that isn't the most dangerous, since teeth are not a vital organ. You can live for many years without any teeth: just look at any old person!

No, the most dangerous prank is when you pretend to be a ghost, and the police try to catch you, because apparently you're not allowed to run around the park at midnight, naked and screaming.