Dong Chim you say? A guide to anal probing

Kancho 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!"
The word is a slang adoption of the Japanese word for enema. In accordance with widespread practice, the word is generally written in katakana when used in its slang sense, and in kanji when used of enemas in the medical sense.
The prank is pervasive in Japan. There are anime glorifying this act (such as the anime Naruto, where it has been called the Thousand Years of Death).

In Japan, there is even a TV gameshow where a celebrity routinely kanchōs random people.
This prank is not exclusive to Japan. In South Korea, it is known as "ttong chim" (also Romanized as "dong chim" or "ddong chim" and roughly translating to "poop needle") and in the Philippines, it is known as "katsibong", "bembong", "bombet", "jempot" or "pidyok", from the Filipino word "tumbong" for rectum. 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.
In February 2006, Nanmon Kaiketsu (Solving Difficult Problems), an NHK TV show about social problems, speculated that the long-term leniency of Kancho is an indirect cause of the rampant train gropings across Japan.

See Also
Boong-Ga Boong-Ga, a video game for the Korean and Japanese market that allows the player to engage in simulated anal probing.