expression, noun
a piece of cake; a cinch; something very easy
Idiomatic expression meaning something is extremely easy to do, often used in a dismissive or humorous tone. Literally 'a kappa's fart', implying something trivial.
See also: 河童の屁
こんな仕事は屁の河童だよ。
This kind of work is a piece of cake.
彼にとっては、試験なんて屁の河童
For him, exams seem to be a cinch.
Literally 'a kappa's fart'. The kappa (河童) is a mythical water creature whose farts were thought to be insignificant and effortless, hence the meaning of something trivial or easy. The exact origin is uncertain, but it is a well-known Japanese idiom.