I think most of us are familiar with the common semantic stopsigns like "God", "just because", and "it's a tradition." However, I've recently been noticing more interesting ones that I haven't really seen discussed on LW. (Or it's also likely that I missed those discussion.)
The first one is "humans are stupid." I notice this one very often, in particular in LW and other rationalist communities. The obvious problem here is that humans are not that stupid. Often what might seem like sheer stupidity was caused by a rather reasonable chain of actions and events. And even if a person or a group of people is being stupid, it's very interesting to chase down the cause. That's how you end up discovering biases from scratch or finding a great opportunity.
The second semantic stopsign is "should." Hat tip to Michael Vassar for bringing this one up. If you and I have a discussing about how I eat too much chocolate, and I say, "You are right, I should eat less chocolate," the conversation will basically end there. But 99 times out of a 100 nothing will actually come out of it. I try to taboo the word "should" from my vocabulary, so instead I will say something like, "You are right, I will not purchase any chocolate this month." This is a concrete actionable statement.
What other semantic stopsigns have you noticed in yourself and others?
I don't know. I read and writ a lot of math (where "obvious" is probably most likely to be overused) and I do try to double-think every time I write it down. But when reading, it means to me "this statement SHOULD be obvious, if it's not, then you're missing something and you should probably reread what just happened." If it doesn't say that and just states the result I am less likely to give it a second thought, perhaps ironically. If they don't say "obvious" then maybe they're quoting some theorem I don't know and that often isn't very relevant unless I need to know every detail of this. If they do say "obvious" then they've at least judged that theorem (or definition or whatever) to be sufficiently basic as to be worth my while learning. Not only that, but if I think something seems obvious and the author thought it was sufficiently obvious to call it obvious, then I'm probably not missing anything subtle!