I remember reading a newspaper article wherein a man handed an umbrella to a fellow pedestrian during a downpour. Grateful, the person quickly opened the umbrella to protect themselves from the rain. And then a plastic spider dropped down on them.
A relatively harmless prank that at most does some mental shock, but got me thinking how you’d do something similar while upping the ante.
Needless to say, please don’t replicate what happens in the story.