Make allusions you decline to explain. Any idiot can deploy a stupid simile: The Republicans are just like the Nazis! Because they, um, favor, um, counterfeiting the GBP to destroy the British economy! Or something! But an unexplained allusion gives anybody who understands it a nice little insider's smile--and causes them to feel a certain affinity for you, as a fellow insider. An outsider who has to go to Wikipedia to figure out what you're talking about will recognize your superior knowledge. Plus, the guy who doesn't get it and huffily responds can be mocked for not getting it. So all around, you've just gained a bit of credibility merely by omitting something. This works best, of course, if you have some kind of clue what you're talking about: the Kursk Bulge does not refer to a submarine structural failure, and if you suggest it does, you look like an idiot.
Use fake imprecision to imply greater knowledge. Another thing any idiot can do is look up dates online. Nobody is impressed that you know that in the first three weeks of July, 1944, 730 delegates from all 44 Allied nations gathered at the Mount Washington Hotel in Bretton Woods, New Hampshire, United States, for the United Nations Monetary and Financial Conference. After all, I cut and pasted the majority of that sentence from Wikipedia. On the other hand, if you can toss off references to Bretton Woods and the gold standard, you can make it appear that you really do know what you're talking about and can just call up the information from memory at will--even if you've only just looked it up on Wikipedia! As with allusions, however, you should be careful only to refer to things you do have some understanding of, lest you look like an idiot.
Treat stupid questions as if they were serious. Has anyone ever asked you "What are YOU looking at?" in a bar or other public place? That person was, of course, looking to do the Monkey Dance, work his way up to chest-poking or hat-knocking-off, and perhaps eventually a sucker punch. Blogging works much the same way--monkey dancing is the dominant mode of commenting. But on the other hand, if you actually try to answer that drunken idiot's question--act as though you don't detect the challenge, point at something and call the questioner's attention to it--you can get inside his OODA loop (unexplained allusion! Look it up, people!) and diffuse a bad situation. In blogging, treating a stupid question seriously can accomplish one of two goals: it can highlight the stupidity (because the answer is stupid, or obvious), or it might (and sometimes has, for me) elevate the discourse by pulling your interlocutor off of his stupid position and into a real discussion. Either way, you win, because you aren't the one being a jerk.
Treat serious questions as if they were stupid. This isn't something I would do all the time. It can make you look like a jerk, and nobody likes jerks. But sometimes an earnest question can present the perfect opportunity for mockery, especially of your opponents. So for instance, when somebody asked recently what can't be regulated by Congress as "interstate commerce," a couple of us replied "abortion and sodomy," or words to that effect. Now, that's not a serious or thoughtful response, nor is it a fair representation of the "liberal" position--which Alsadius later pointed out should have included marijuana--but it was a good opportunity to score a cheap point and maybe get a laugh or two. And frankly, it wasn't so far off; in the course of that discussion at least two commenters said to me that they thought the commerce clause power was restrained only by the affirmative prohibitions of the bill of rights--one went so far as to say that Congress could, consistent with the Constitution, implement Communism under the commerce power. So it's hard for people who disagreed to complain about unfairness, and people who were inclined to agree got a chuckle. Overall, a win.