The story
From Japanese カンチョー (kanchō), from 浣腸 (“enema; to give an enema”), from 浣 (“to wash, washing”) + 腸 (“bowels”).
Etymology from Wiktionary, CC BY-SA 4.0.
kancho
Today it means: A prank among children in East Asia in which one's fingers form the shape of a gun and one tries to ram them into the anal region of an unsuspecting person. Full definition →