r/Fitness does a weekly "Moronic Monday", a judgment-free thread where people can ask questions that they would ordinarily feel embarrassed for not knowing the answer to. I thought this seemed like a useful thing to have here - after all, the concepts discussed on LessWrong are probably at least a little harder to grasp than those of weightlifting. Plus, I have a few stupid questions of my own, so it doesn't seem unreasonable that other people might as well.
I wish I could upvote this question more. People assuming that I meant more than exactly what I said drives me up the wall, and I don't know how to deal with it either. (but Qiaochu's response below is good)
The most common failure mode I've experienced is the assumption that believing equals endorsing. One of the gratifying aspects of participating here is not having to deal with that; pretty much everyone on LW is inoculated.
Be cautious, the vast majority do not make strict demarcation between normative and positive statements inside their head. Figuring this out massively improved my models of other people.