李下に冠を正さず
(Rika ni kanmuri wo tadasazu; “Don’t straighten your hat below a plum tree”)

Definition:

Don’t do things that invite suspicion or misunderstanding. Even if you’re innocent, it’s best to avoid even the accidental appearance of guilt. If you reach up to adjust your hat below a plum tree, someone at a distance might think you’re stealing plums – so you’re advised to take care of the hat somewhere else just in case. For example, if you’re not guilty of crimes, it’s best not to act like you’re doing your best to obstruct justice in a desperate cover-up.

Breakdown:

We begin with the unusual compound noun 李下 (rika), “below a plum tree.” It’s marked as location by the particle に (ni), followed by the noun 冠 (kanmuri), often translated as “crown” but in this case referring to a more esoteric kind of headwear (although its use was likely restricted to the aristocracy). This noun in turn is marked as the object of a verb by the particle を (wo). And the verb in question is 正す (tadasu), “to correct” or “to straighten,” in imperfective form with a negative ending that could be interpreted as either conjunctive or sentence-final.

Notes:

This saying comes to us from a Chinese poetic collection predating the Six Dynasties era, known as the 古楽府 (in Japanese, Kogafu). It’s part of a longer phrase in which it follows 瓜田に履を納れず (kaden ni kutsu wo irezu), “Don’t adjust your shoes in a melon field.” Both phrases together can be boiled down to the four-character compound 瓜田李下 (kaden rika).

The character 正 can be replaced with 整 without any change in meaning or pronunciation.

The original 冠 was a pretty funky kind of hat:

Example sentence:

「ただの失敗だからこそ、隠さずに早く謝りに行った方が良いんだよ。瓜田に履を納れず李下に冠を正さずだからね」

(“Tada no shippai dakara koso, kakusazu ni hayaku ayamari ni itta hou ga ii nda yo. Kaden ni kutsu wo irezu rika ni kanmuri wo tadasazu dakara ne.”)

[“All the more because it was just a mistake, you should go apologize right away instead of trying to cover it up. You don’t want to accidentally make yourself look guilty of real wrongdoing, after all.”]