The Japanese term for this very classy act is Kancho. Kancho is performed by clasping the hands together so that the index fingers are pointed out, and then inserting them into someone’s anal region when they are not looking.
If the attack is successful, then the offending party is meant to scream “Kan-CHO” (emphasizing the second syllable). The prank has been featured in anime such as Naruto and there is even a game show where a celebrity routinely kanchos random people. It is also prevalent in South Korea, Taiwan, and Vietnam.
In certain countries however, like the United Kingdom, it’s considered sexual harassment and is therefore illegal. Kancho is a slang version of the Japanese word for enema. Each country has its own term for the prank. In Korea that term roughly translate into “poop needle.” In England the prank is referred to as “aimage.”
In the Phillippines, the prankster says “Rayyyy....GUN” and then executes the prank. And in Israel the term roughly translates into “My God, what is this shit.”