I have no information or record of anyone putting a pie with gentian violet in their fridge as a prank. It's possible that such an event occurred or that it's a fictional or localized incident that didn't gain widespread attention.
Gentian violet is a dye and antiseptic agent used for various purposes, including medical applications and as a stain in laboratories. It's not a typical substance used in pranks due to its staining properties and potential health risks if ingested. Pranks involving harmful substances are not only irresponsible but can also be dangerous.
If you have heard of such an incident, I recommend verifying the information from reliable and up-to-date sources before drawing any conclusions. It's essential to prioritize safety and ethical behavior in any practical jokes or pranks.