(Not a cup of sugar, mind you. Just a cup.)

人の褌で相撲を取る
(Hito no fundoshi de sumou wo toru;
“Doing sumo in someone else’s loincloth”)

Definition:

Using something that belongs to someone else for your own benefit or profit. Taking advantage of somebody else’s tools, work, or other resources for personal gain. This saying does not apply to situations such as support that someone else offered unlooked-for. It carries a strong implication of using the people around you in an underhanded way to cheat or cut corners. Like borrowing somebody else’s ritual sumo garment to compete in, perhaps because you were too lazy or stingy to just buy one of your own.

Breakdown:

We begin four characters in, with the particle で (de). In this case, the particle marks the means by which an action is performed, and that means is the noun 褌 (fundoshi), “loincloth.” What loincloth in particular is specified by using associative particle の (no) to connect it with noun 人 (hito), “person.” (In this case, the term takes on the nuance of “some random person,” “somebody else (whom you wouldn’t have expected to be involved).”

Moving in the other direction, the verb phrase performed with someone else’s loincloth starts with the noun 相撲 (sumou), “sumo wrestling.” The particle を (wo) marks this as the direct object of the actual verb; the proper verb in Japanese for “doing” sumo turns out to be 取る (toru), literally “to take,” here in conclusive form.

Notes:

Alert readers will remember seeing the character 褌 with a different reading not too long ago.

This saying comes to us from 『滑稽四十八癖』(Kokkei shijuuhachi guse), an 1885 text by comic writer Shikitei Sanba (式亭三馬). (The work’s title may ring a bell as an allusion to the extended form of this saying.)

Some variants make the nuance of 人 explicit by replacing it with 他人, “another person,” “others.” This compound may be pronounced tanin or, as above, hito. In the context of this kotowaza, sumou can also be written 角力, apparently without any change in meaning pronunciation.

Example sentence:

高校の間ずっと人の褌で相撲を取るように、エッセイを書くことになったら、友達から借りた資料だけで書いていたジョンは、大学生になってすぐ単位を落としてショックを受けた。

(Koukou no aida zutto hito no fundoshi de sumou wo toru you ni, essei wo kaku koto ni nattara, tomodachi kara karita shiryou dake de kaiteita Jon wa, daigakusei ni natte sugu tan’i wo otoshite shokku wo uketa.)

[John, who through all of high school had ploughed his fields with other people’s calves by only using materials borrowed from his friends when it came time to write an essay, received a shock when he failed a class immediately after entering college.]