He Demonai (屁でもない - Nothing)

If you want to express "it's not a problem at all" or "it's so easy," you can say the Japanese term "he demonai" (屁でもない).

The "he" (屁) means "fart" and the "demonai" (でもない) means "inferior to," so the literal meaning of this term is "it's inferior to a fart."

This term comes from the thought that things that are inferior to a fart will never become a problem.

Incidentally, there is a Japanese slang term, "he no kappa" (屁の河童), which also contains "he" (屁 - fart).

The etymology of this slang term is not related to "fart," but this has the same meaning of "he demonai."
http://lang-8.com/kanotown/journals/191665208695223752666684613979550944204

屁でもない

「全く問題にならない」ことを表現したいとき、「屁でもない」という言葉を使うことができます。

「屁」は "fart," 「でもない」は "inferior to" を意味するので、「屁でもない」は "It's inferior to a fart" という意味になります。

屁にも値しないようなものは、とるに足らないようなことであるということです。

ちなみに、同じ「屁」を使った俗語に「屁の河童」があります。

こちらは "fart" を語源にしていませんが、意味は「屁でもない」と同じです。
http://lang-8.com/kanotown/journals/191665208695223752666684613979550944204

• If you want to express "it's not a problem at all" or "it's so easy," you can say the Japanese term "he demonai" (屁でもない).
• If you want to describe something that is simple and easy to accomplish, you can say the Japanese term "he demonai" (屁でもない).

Interesting! Speaking of farts, there is an expression "Not worth a fart" or "Not worth a fart in a whirlwind" that means that something is completely worthless.