Dan's final comment succinctly calls out the situations which irk me the most. You asked me how I'm doing. I answered honestly... and now you're going to judge me for that? Yeah, nah. I'd rather just not answer at all, thanks, instead of dealing with that bullcrap.
Which, over the course of time, led me to the analytical conclusion that more often than not, most people don't actually care how -- or even if -- I answer at all, unless I make the "mistake" of answering honestly when I'm not feeling perfectly peachy. That's why I almost always answer with something vaguely nonsensical when asked how I'm doing by random strangers, such as, "Howdy, howdy!" Most of them are so locked into their autopilot that they only ever hear that first syllable, and immediately think I just asked them how they're doing... so they reflexively toss back their obligatory, "Oh, I'm fine." Once in a blue moon, one of them will skip a beat and realize what I actually said just after their reply, making the passing interaction vaguely uncomfortable for them. Which, you know... is actually just fine by me, since that's how I feel almost all the time.