I finally had my first genuinely random run-in with another Head-Fier last night.
I hosted a party at my house, and had somebody else handle the invites because I was out of town when the idea was established. Because of that, a few of the people who came were friends of friends I'd never really talked to before. A few hours into the party, we got rained out and all end up clustered in my living room, kitchen and bedroom. I showed off my collection of music on CD and vinyl since a large percentage of the people there appreciate good music, and I had some decent tunes going in each room. Somebody asked me about a Dave Matthews Band live album they hadn't heard before, and since I didn't want to interrupt the flow of music already in the room I broke out the portable setup instead, which at that time was a really sturdy Panasonic portable CD player coupled with a CMoyBB and sent out to my Mad Dog V2.
As I got all the cords plugged in and turned down the background music a bit to help with isolation, the guy who asked about the album mentioned something about "audiophile quality headphones" in a very generic fashion (perhaps he was testing the waters). At that, I mentioned how I considered myself an audiophile, and pointed out a few places in the room where I stashed my gear. He seemed very interested, and mentioned that he had a few pairs of high-end headphones of his own but that he was just getting into the hobby.
As we talked it turned out that he had an M50 (which I guessed correctly that he owned before he told me), as well as a Shure SE315 for drum monitoring. He doesn't actually have a Head-Fi account, but he's a longtime lurker who finally started buying stuff recently. He was more than just a casual M50 owner; he knew about my amps and was familiar with various headphone brands, and for the first time in my life I found myself having an in-depth headphone conversation outside the realm of a meet.
I guess this isn't really a headphone sighting at all, but meeting an enthusiast is even more important than seeing his gear in public.
TL;DR A house party being rained out led to my discovery of a Head-Fi lurker among friends.