鴨が葱を背負って来る
(Kamo ga negi wo shotte kuru;
“A duck comes bearing a green onion on its back”)

Definition:

A confluence of almost-too-good-to-be-true convenience. Often used when somebody you’d been planning to use or con comes to you with a get-rich-quick scheme; when suckers come to you essentially asking you to take their money. Like a duck that comes for dinner, bearing ingredients for its own cooking on its back.

Breakdown:

We begin with the noun 鴨 (kamo), “duck,” marked as the subject of the sentence by the particle が (ga). Next comes the noun 葱 (negi), a long vegetable akin to Western green onions or leeks, marked as the direct object of the verb by the particle を (wo). What follows is all one verb phrase. It comprises the verb 負う (ou), “to carry on one’s back,” in conjunctive form, combined with the noun 背 (se), “back,” followed by the verb 来る (kuru), “to come,” in sentence-final form.

Notes:

Note that while one might expect 背負って to be pronounced se.otte based on its parts, the slurred form shotte is considered correct for this kotowaza.

This entire phrase can be condensed into the two-character noun 鴨葱 (kamonegi).

The surface meaning apparently leads some people to use this phrase to thank others for helping them out, but the deeper connotations mean that doing so is actually pretty rude.

Example sentence:

「中田の奴に会えて良かったなぁ。今日の売り上げはさっぱりだと思ったら、ちょうど鴨が葱を背負って来たぁ」

(“Nakata no yatsu ni aete yokatta naa. Kyou no uriage wa sappari da to omottara, choudo kamo ga negi wo shotte kitaa.”)

[“I’m glad I ran into that Nakata guy. I was just thinking I wouldn’t have any take today, when the sucker fell right into my lap with a ribbon on top.”]