杯酒解怨（はいしゅかいえん）

cup : sake : solution : grudge

Who's to say a little enmity can't be solved by sharing a pint? Certainly not Li Sheng, to whom the origin of this yoji-jukugo is credited. Today's proverb comes from the New Book of Tang: an official chronicle of one of the golden ages of Chinese history, the Tang Dynasty (ca. 618–907).

杯酒解怨 is defined as: "washing away all enmity and ill will by sharing a drink". It first appeared during a confrontation between military general Li Sheng and Chancellor Zhang Yanshang. Having long held grudges against each other (over a woman, no less), it appeared as though the two had finally begun to make amends after the Zhu Ci rebellion; however, upon Li's request that Zhang give a daughter to one of his sons for marriage, he refused. Still apparent that Zhang harbored ill will towards him, Li commented:

"For I am a military man, I choose to forget old grudges against someone after I have shared a drink with them. Those who call themselves Confucians are not so; though they may appear peaceful on the outside, they hold anger in their chest. That you would refuse the marriage is because you have not forgotten our former quarrel, is it not?"

As much as this would make for a wonderful soap opera, the key point to take away is that—among its other reputation as the cause of many a quarrel—alcohol was apparently also regarded as the solution to many friendship problems. And unless I'm much mistaken, that pretty much still holds true today.

My attempt at a four-word translation of 杯酒解怨

Drink 'Til You're Friends

弱肉強食（じゃくにくきょうしょく）

weak : meat : strong : eat

After a lengthy hiatus, I'm back to introduce a yoji-jukugo so comically well known that quite a few non-native Japanese speakers should have already heard of it: 弱肉強食. Fully stocked with two preexisting 4-word translations, 弱肉強食 is defined as the "law of the jungle", or the "survival of the fittest". Han Yu—arguably known as the Chinese Shakespeare of his time—is credited with coining this term in his literary work, Preface Seeing Off the Buddhist Wenchang. 

This particular yoji-jukugo has been indoctrinated into a group of comedic Japanese known as proverbial parodies. Some of these parodies take advantage of homophonous kanji to change the meaning while preserving the pronunciation—such as 馬子にも衣裳 (まごにもいしょう, "anyone can look good with the right clothing"), which can be hilariously miswritten as 孫にも衣裳 (same pronunciation, "even your grandchildren can look good with the right clothing"). Meanwhile, others change a few words here and there while keeping the core rhythm of the expression intact: for example, 寄らば大樹の陰 (よらばだいじゅのかげ, "If you seek shelter, look for a large tree") has been given a not-so-subtle edit to reflect modern sentiments in business-era Japan as 寄らば大企業 (よらばだいきぎょう, "If you seek job security, work for a large firm"). 弱肉強食 falls into the latter of those two categories, thanks in large part to a slight formatting flop in Japanese standardized testing a couple decades back. 

It is common in Kanji Kentei to test yoji-jukugo proficiency by omitting one or two kanji from the proverb and asking the participants to fill in the blanks. In the latter half of the 1980s, 弱肉強食 was often depicted on tests as ○肉○食, tricking children across the country into foolheartedly writing down 焼肉定食 (やきにくていしょく), or "set meal with grilled meat". It became such a common mistake that critic Hideo Okuma included it in his book How to Write Understandable Japanese (unofficial title translation), noting that he was struck dumbfounded when students provided no explanation other than "that's all I could think of".

Playing along with the proverbial parodies (and since we already have two fully functional 4-word translations of this proverb), I'll make a couple puns out of this one.

My attempt at two parodies of 弱肉強食（焼肉定食）

Survival Of The Fattest

Law Of The Cafeteria