For me, it was eating too fast. Ironic, since as a kid, I ate way too slow, so my parents said in fact that was one of the things that caused them to realize that I was "different" from other kids.
I was unwittingly turning off prospective dates/partners with that - it wasn't till after my diagnosis that I learned to gauge my speed (and their facial reaction!) better, so now I've got a wife and kids which I may not have had otherwise!! And she still criticizes me occasionally of eating too fast, as did my in-laws (aaargh...)
Tangent alert (!) I chuckled at Fnord's signature line, "I don't take vague hints, or subtle hints, or strong hints etc.." and then I thought, Fnord wouldn't do so well in Korea. When I read Malcolm Gladwell's "Outliers", he explained why Korean Airlines crashed more than the average airline, because the co-pilot wasn't allowed to contradict the chief pilot, even when the chief pilot was making errors due to lack of sleep - the co-pilot could only make vague hints, subtle at most, so that the pilot would "save face". In other countries' airlines, the co-pilot could criticize and correct more freely. Ahhh, but of course, Qantas has never crashed before, no definitely never crashed, nuh-uh, no crashes, yeah