Etymology Calque of French soixante-neuf, from the rotational symmetry of the numeral 69 — if rotated a half-turn (by 180°), the numeral remains the same, and a couple both giving oral sex at once have, in principle, a similar rotational symmetry.
1
Lifestyle, Sexuality A sex position where two people perform oral sex on each other simultaneously.
Dearest Annabelle, Having a splendid time! Last night I did a sixty-nine with Antonio that went on for HOURS. Later I even let him go in my back door, if you know what I mean, wink wink. I love that man’s tool so much! Much Love, Aunt Ruth2005, Annabelle du Fouet, “Introduction: How this book came to be”, in Weather Balloons Make Rotten Sex Toys, Ellora's Cave, →ISBN, page 10:
sixty-nine
verb
Etymology Calque of French soixante-neuf, from the rotational symmetry of the numeral 69 — if rotated a half-turn (by 180°), the numeral remains the same, and a couple both giving oral sex at once have, in principle, a similar rotational symmetry.
1
Slang To have sex in the sixty-nine position: to engage in mutual oral sex.
One of my old lovers liked to sixty-nine because the distraction of what she was doing kept her mind off what she was feeling so that her anxieties about what right she had to feel so good could not as easily keep her from feeling it.1976, Marilyn Gayle, What Lesbians Do, Amazon Reality Collective:
You pat me on the head / You took me out to wine, dine, sixty-nine me / But didn't hear a damn word I said1995, Alanis Morissette, “Right Through You”, in Jagged Little Pill: