Late 90's, flying US with my mother from LGW to CLT. Separate PNR's...me on a paid ticket, her on an award using my miles. Flying Y, in exit row because I was Gold.
I dropped her off at the terminal before I went to dump the rental car. I told her if there isn't a long queue, go ahead and check yourself in to get rid of your bag. If it's a zoo, wait for me and we'll use the elite queue.
I come back to the airport a half hour later, and she's sitting there with her J BP.
I ask how the heck that happened, and it turns out I had been systematically upgraded due to an oversell in Y. (She must have asked to confirm I was still in the seat next to hers.) So she talked her way into the seat in J next to mine!!
No status, rather infrequent flier in general, on the basic (low) Y award!!! I have *never* been able to pull that off myself.