No, please, I couldn’t possibly. Sorry. No, no, no. Thank you. Sorry.

礼も過ぎれば無礼になる
(Rei mo sugireba burei ni naru;
“Even politeness, when overdone, becomes insolence”)

Definition:

An overabundance of manners and deference becomes rude. Even for something as valuable, and as fundamental to the proper functioning of society, as good manners, there can be too much of a good thing.

Breakdown:

We begin with the noun 礼 (rei), “ceremony,” “reward,” “thanks,” “etiquette.” This is followed by emphatic particle も (mo), here serving as “even,” and then the verb 過ぎる (sugiru), “to [sur]pass,” in a pseudo-conjunctive form* and taking the hypothetical suffix ば (ba), “if” or “when.” The following independent clause ends with the verb なる (naru), “to become,” in conclusive form. This is preceded by the directional particle に (ni), which tells us that what 礼 becomes is the noun 無礼 (burei), “rude[ness],” literally just a negation of 礼.

Notes:

The first image that popped into my head was an error: I imagined someone deliberately and mockingly using the forms of politeness inappropriately for the social context to give offense. But my sources paint a picture based on the practical downsides of extreme obsequiousness: even when no offense is intended, it can be a pain having someone checking in on your mood constantly, asking how you want things done, and so on.

*The classical base form of the verb is 過ぐ (sugu); 過ぎ (sugi) was both the imperfective and conjunctive forms. In this case, it acts as the imperfective and takes the passive particle る (ru), which in turn takes conjunctive form as れ (re).

Example sentence:

「あの後輩は…気遣いできるのはいいんだけど…細かいところまで何度も聞かれるのはちょっと…。ほんと、礼も過ぎれば無礼になるよね。」

(“Ano kouhai wa… kidzukai dekiru no wa ii nda kedo… komakai tokoro made nando mo kikareru no wa chotto…. Honto, rei mo sugireba burei ni naru yo ne.”)

[“That underclassman… it’s good that they know to take other people’s feelings into consideration… but getting asked about every little thing is a bit…. Being too polite is a kind of being rude, you know?”]