If people have the choice to mind their own business i consider it a proper prank.
its when the pranker is openly antagonizing and harassing someone that i feel like they cross a line.
For example, If i don't know its a prank and you snatch my wallet, i kinda have to participate whether i like it or not.
Seeing this would scare you if you are a person with any amount of empathy for others but ultimately you aren't forced to do anything about it.