Several times since I've been here and on a certain other community, topics have come up about interracial dating, and usually refusing to do so warrants 'BUT IT'S THEIR PREFERENCE!' (Note that this means REFUSING to do so, not simply not having done so or not particularly inclined to do so, to avoid any wank on the subject) Often it somes up that it's a preference just like any other physical feature.
So, AMA, is there any PHYSICAL feature (body shape, hair color, skin color, height, etc) that would make a person of your preferred gender* absolutely undatable under any circumstances, regardless of their personality, your chemistry, and everything else that makes a relationship work? And not just in a way that you'd say 'well, I'd never approach a redhead' or 'a tall person wouldn't catch my eye.' Assume that you know this person beyond just their looks.
*(because gender and other species aren't even remotely in the same category, no matter how much people say it is)
My answer: I think that at a certain point, if they were so obese that they couldn't do everyday things, I couldn't handle it. While I don't find heavy guys attractive in general, I could date an overweight guy. But my SO needs to be able to keep up with me and such.