What is Kanchō

Kanchō (カンチョー) is a Japanese prank (also known as ddong chim in Korea) performed by clasping the hands together in the shape of an imaginary gun and attempting to poke an unsuspecting victim's anus, often while exclaiming "Kan-CHO!".

The word is a slang adoption of the Japanese word for enema (浣腸 kanchō).

In accordance with widespread practice, the word is generally written in katakana when used in its slang sense, and in kanji when used for enemas in the medical sense.

It is a form of prank among children in East Asian countries such as Japan, Korea, and Taiwan, etc. In Korea, it is called ttongchim.(똥침)

In Taiwan, it is called Qiānnián shā (千年殺).

Source: https://en.wikipedia.org/wiki/Kanchō