That grandiose title is simply meant to convey that people can be stupid about some things and not others. I enjoy a good collection of people saying stupid things on the internet as much as anyone; this one, for example. All of these are cases of people being too ignorant for most people even to fathom, but let's consider how they are being ignorant for a moment.
Several are, of course, about spelling, or knowing the sound of a word without thinking of what it really represents: "hall of cost" for holocaust, "meaty oaker" for mediocre (that one gets me every time), "flaming young" for filet mignon, "synonym rolls" for cinnamon rolls, "Rosetta Stone" for Rosa Parks. Although they evince terrible spelling, in none of these cases is the person getting the meaning wrong because of misunderstanding the root. The last one is not so much spelling as a person who has heard a name getting it mixed up with something that sounds similar.
Some do show a real misunderstanding of the concept, such as thinking that chicken and turkey are the names of meats without knowing that they are also animals (I know, how is that possible?), thinking squirrels and/or dolphins are reptiles, referring to a "morning sunset," or thinking that "rotating tires" refers to the same kind of rotation that happens as you drive. All of these are people who probably would know better if they thought about it, or at least would recognize how silly they sound once it was explained. It's not hard to see how someone might slip and write "morning sunset," and although it's hard to see how someone could think squirrels or dolphins are reptiles, it's probably a case of someone trying to come up with what group both animals are in and not stopping to think that the first thing that occurred to him was a very bad answer. The mistake about rotating tires is perfectly understandable if you have never thought about the subject before. The mistake was to think that there wasn't some other meaning to the term: if it seems ridiculous to pay someone to rotate your tires because they constantly rotate themselves, yet people seem to do it, you're probably not understanding something. This is one of the most common mistakes I have noticed, and it is particularly noticeable among comedians. They pick something that seems silly on the face of it and treat it as though it really is as illogical as it appears. Sometimes, I know, they say these things in mock ignorance, but there's no doubt that a lot of comedians think they have really hit on something insightful when they make these jokes. That's why I'm wary of political comedians: because political issues are usually complicated and, like anything relating to people's collective behaviour, have a lot of subtlety and unspoken assumptions behind them, they can be easy targets. However, the simplified version you get from a comedian is probably missing out on a lot of the key issues, so this dumbs down the debate. I'd rather people stop and think about the problems that aren't obvious than that they learn a quick quip with which to cut down their opponents without really saying anything useful.
Enough of that rant. Some of these dumb statements show a lack of common sense. The classic case is the person who falls for the idea that he can recharge his cell phone in the microwave. There are a lot of things that aren't intuitive about technology, so you can't really blame this person for not being sure that it wouldn't work. The problem is more that he didn't stop to consider the likelihood that someone was trolling him and double check before risking his phone in an experiment. From a few old wives' tales we now have a huge collection of "urban legends," many of which, I'm sure, start out with people deliberately trying to confuse the issue. There is a lot of useful advice on the internet, but you should stop and think about any of it before proceeding. If you're not going to double-check, at least consider the possible consequences of being trolled. It's not too bad to have your time wasted on something useless, but losing a phone to a prankster is frustrating.
One person asks if it takes 18 months for twins to be born. You would think that a brief consideration of what's going on inside the womb -- the developement of a fetus -- would show you that two babies develope at the same time and not one after the other. It's a silly mistake, but not so silly that it is inconceivable that someone might wonder. Remember this when they tell you there are no such things as stupid questions. (Hint: they don't really think that.) Another person asks if styrofoam earplugs are rubber bullets. Heck, if I didn't recognize them as earplugs, I might think they were rubber bullets. If a person hasn't seen them in context before and just finds a few on the street, how would he know better? The same logic goes for the person who thought "Titanic" was a movie rather than a re-enactment of an historical event. Sure, we've all heard of the sinking of the Titanic...or maybe not all of us have. Is it really a sign of such great ignorance not to know this relatively minor piece of history? I've seen movies before where I looked up to see if they were historical or not. They weren't as well-known as the Titanic, but someone could easily think I was ignorant for not knowing the history.
What I'm trying to get at here is that, while these statements all seem literally unbelievable, the people who made them may not be as clueless as they seem. I have huge blind spots about some things, and I'm sure I've come off as equally ignorant. The first wedding I ever attended on my own, I didn't realize I was supposed to get a present for the couple. I had never been to a wedding where my parents hadn't taken care of that detail, and it never occurred to me. It is reasonable to think that someone would pick up that knowledge by age 20, but it doesn't require great stupidity not to learn it. We all have limited amounts of attention to spend on learning things, and we all have different interests and strengths. With such a broad scope to "common knowledge," it is hardly surprising that people don't pick up one aspect or another of things that most people take for granted. Sure, if you stop to think about something, you might realize that the ideas you have been harbouring for years are dubious, but the whole point is that we don't stop to think about everything. We can't, even if we wanted to. And social media lends itself to rapid, instinctive responses. You would rarely see these comments in a book, or even an article, because they would have to go through a process to get published. When someone blurts out the first thing that occurs to him, you're bound to end up with some mistakes that sound really silly. But as you're laughing at them, don't forget that you could sound equally silly on some subject that you haven't had occasion to post on social media about.