'Your mileage may vary' — the disclaimer from petrol adverts, adopted by Usenet as the polite way to say 'this worked for me and might not for you'. The record's entry for the oldest hedge still in use, and the only one from a car commercial.
I saved a screenshot of the first YMMV post I saw. Looking at it now, the joke is entirely in the timing. The timing does not survive the screenshot.
The record notes YMMV has been typed for thirty-five years by people who have never seen the advert, which is the record's definition of a phrase that has fully escaped.
What does it mean? Write it the way you would say it out loud.
