Today the Beatles had their annual Christmas party, a Magical Mystery Tour–themed event to which everyone wore costumes.

Hip and glamorous though it was, attended by all of Swinging London’s most beautiful people, this shindig had one thing in common with every office Christmas party: someone got roaring drunk and ran amok. In this case, that person was John Lennon.

According to one in-depth account,

Lennon was, by all accounts, a terrible drunk, and on this night, John was chugging them down.

Patti Harrison, an ex-model, is usually acknowledged as the most beautiful of all the Beatle wives. Patti, like many women at costume and Halloween parties, went all out and was dressed up in an incredibly sexy, revealing outfit and John Lennon was “all-eyes.” Accounts of the party say John was leering, ogling, and flirting with Patti from the word go.

All this happened in full view of John’s wife Cynthia; eventually the situation became so awkward that the singer Lulu publicly berated Lennon, who apparently sat there and took it like a shamefaced little boy. Where George was while all this was going on, I have no idea. (He may have been chasing Maureen Starkey — pictured above in a very dated Indian costume — with whom he would later have an affair.)

In truth, though, a lot of John’s erratic behavior during this period had to do with someone other than Cynthia or Patti, someone who was not present at this party. You know who:

Yoko Ono had been “particularly persistent” in her pursuit of John Lennon since their first meeting at her Indica Gallery show in 1966. Over the course of several months thereafter, she had tried unsuccessfully to get his attention, first standing at the gates of Kenwood [John’s estate] among the horde of groveling fans and haunting the steps outside the Apple offices, in the hope of a “chance” encounter. She once gained admittance to Kenwood for the purpose of calling a taxi, then planted a ring by the phone, necessitating a return visit. Cynthia recalled that afterward, “there were a lot of phone calls [at home] from Yoko, and John received a constant flow of letters from her,” none of which aroused Cynthia’s suspicion – or his, so it seems. “John read them and left them lying around.” [Bob Spitz, The Beatles]

In addition to the personal letters, John received a series of postcards that were part of an art project called “Dance Event.”

Different cards kept coming through the door every day saying “Breathe” and “Dance” and “Watch all the lights until dawn,” and they upset me or made me happy, depending on how I felt.

Slowly and gradually, Yoko got into John’s head, where she would remain for the rest of his days. He came to regard her less and less as “crackers…just a weirdo artist,” which he called her at one point, and more as a bold provocateur whose iconoclasm matched his own.

At this point their relationship was strictly intellectual, consisting of secretive late-night phone calls; it would take months to evolve into a physical one. In retrospect, it seems possible that John intentionally chose tonight to begin the process of disentangling himself from Cynthia…it’s also possible that he just got wasted and let his id run rampant. In any case, by the time the next Christmas rolled around, things would be very different.