Pythagoras advised followers to “abstain from beans because they are flatulent and partake most of the breath of life; and besides, it is better for the stomach if they are not taken, and this again will make our dreams in sleep smooth and untroubled” (Diogenes Laertius, Lives of Eminent Philosophers, 8.1.24).

Later, in a passage insinuating that the problem with the beans potentially resided in mystic ritual purification issues, Diogenes Laertius wrote that Pythagoras called for, “abstaining from meat and flesh of animals that have died, mullets, gurnards, eggs and egg‑sprung animals, beans, and the other abstinences prescribed by those who perform mystic rites in the temples” (Lives of Eminent Philosophers, 8.1.33).

Finally, in terms of potential symbolic reasons for the bean ban, Diogenes wrote, “According to Aristotle in his work On the Pythagoreans, Pythagoras counselled abstinence from beans either because they are like the genitals, or because they are like the gates of Hades . . . as being alone unjointed, or because they are injurious, or because they are like the form of the universe, or because they belong to oligarchy, since they are used in election by lot” (Lives of Eminent Philosophers, 8.1.34).

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This is "God Impregnated me" level unhinged, but with lower stakes. I infer he may have farted once with an attractive partner and it scarred him.