Exactly. I would be far more ok with a social norm that condoned introducing oneself to (and starting conversations with) people on plans if there was also a social norm that condoned saying "I don't want to talk to you. Kindly go away and leave me alone." Current social norms regard this as rude. (I take it our esteemed extrovert colleagues see the problem here.)
Datapoint: I don't care for Achmiz's hostility but I do agree with his point here. There is no polite way to explicitly tell someone you don't want to communicate. This is a bug that should be fixed. It harms both parties; the silent one can't indicate that without paying a social cost, and the talkative one can't really be sure they're not annoying their counterpart.
(it is possible the talkative one doesn't actually care if they're annoying their counterpart. If so, fuck them.)
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.