Some goodly number of years in the past, when two friends of mine from the science fiction club at the U of I hadn't been married long, Mary had a nasty stomach flu on Thanksgiving. As Rolf watched her dejectedly eating her little cup of Jello while everyone else was having the feast, he promised her a real Thanksgiving dinner when she could eat it. So he threw a Thanksgiving dinner the following summer. And invited a bunch of friends, who probably would have liked to join them for Thanksgiving at the traditional time, but had other obligations. But they didn't have those obligations in July, so they came. And it was good.
So they did it again the following year, and of course it became a tradition. It moved to May because the party is mostly outdoors (they have a fairly large house, but they have a larger circle of friends), and the weather is pretty nasty in Champaign in July. And most of the original participants have moved away, and only some of them still come back to Champaign, but new people have been added, and it's still a good time.
I ate way too much, of course; it was good, of course. That's the point of Thanksgiving dinner, whenever you have it. Had a good time showing off pictures I'd taken and taking more. Got to spend time with a number of friends, most of whom I don't stay in touch with very well; starstaf and beamjockey are the only ones I know of being LJ users, so it's probably useless to mention anyone else by name.