Kancho (カンチョー, kanchō?) is a prank often played in Japan; it is performed by clasping the hands together so the index fingers are pointing out and attempting to insert them sharply into someone's anal region when the victim is not looking. It is similar to the wedgie or a goosing, although, as compared to kancho, the former mentioned acts do not involve physical contact which is quite as intimate or direct. A Kancho is often executed simultaneously as the offending party loudly expresses the second syllable of "Kan-CHO!"
Did you know that's an actual game played by young Japanese children? Essentially, it's their equivalent of American kids' games like sneaking up behind somebody and yelling "wedgie!" while you hike their underwear up, or yelling "noogie!" while you rub your knuckles on their head.
Kancho - it is such a common joke in Japan, when an unsuspecting victim put a finger in the ... butt.
"This is the dreaded Kancho. When you are distracted and looking the other way a man will come up from behind and shove the Kancho right in your butt. As the man does this he yells Kancho. Please do not try this at home. The Kancho must only be done by experienced individuals with many years of training."
In certain countries, the act of kancho may be illegal and considered sexual harassment, or even sexual assault, although children are given more leniency. While the practice is known in South Korea, there have been cases where adults performing it have been arrested. However, in Japan it is considered a childish prank rather than a criminal act.