What is "denkianma"

Denkianma is a popular Japanese prank played between two people where one person puts their foot into the genital area of the other and shakes it in a vibrating motion. Often this is done by grabbing the other persons two feet to complete the action. This is often done between school aged boys as a prank similar to Kancho and could be seen by a western audience as a type of bullying. Recently the crisps company Doritos released a new flavour of potato chip called "Denkianma"