The three kinds of stupid
Statistically one out of every two people is stupid (ie in the dumber 50th percentile), and even those that occupy the smarter half of the population will find that still others are smarter* and so on. So stupidity is ordinal, and relative, like velocity it depends on the viewpoint of the observer. Regardless of point of view, stupid people can be broadly classified as one of three types, Type One, Type Two and Type Three.
Type One Stupid people are your regular stupid people. They know and we know they are stupid. Found everywhere, usually in the way, doing stupid things such as buying 20 bucks worth of lottery tickets and scratch and wins daily, cruising along at five under in the fast lane while yakking on their cell phone, those big box store employees that can't tell you where anything is, the ones who get their 15 minutes of fame 30 seconds at a time guest starring on COPS... In other words they are you and me. Type Ones, like most of us, are not evil, but the consequences of human stupidity are responsible for way more of the world's ills than the intent to do harm. Type One Stupidity just steamrollers along flattening everything in its path like a Caribbean hurricane, natural, predictable, and mostly avoidable by the nimble.
Type Two Stupid people know they are stupid, but don't want anyone else to know, so they study what they think smart people do and say and imitate them. This is about as convincing as you might expect, but it is also easy to get away with, as it isn't necessary to fool smart people when there are so many credulously stupid ones. Credentials are a fine way to disguise stupidity. You don't have to be very intelligent to get an undergraduate degree, you just have to turn in your assignments and avoid taking courses like quantum mechanics. With an undergraduate degree in hand, it is even easier to get an advanced degree, there is a whole industry out there that will grant a more or less legitimate Masters or PhD, for which the primary requirement is the ability to pay exorbitant tuition fees. If that is too much expense and trouble, make those qualifications up. With the correct qualifications a Type Two can enter a suitable formal profession, a great place for the not so smart, because the professions have powerful associations to protect members from internal and external criticism, and the legislated exclusive right to practise, and a code of ethics whose function is mostly to tame the hurly burly of fair competition. Type Twos who have mastered sycophantry, backstabbing, sandbagging and similar tricks can advance to the highest positions in large (the bigger the better) organizations of all types, public and private, without benefit of talent or smarts. Type Two Stupid can be dangerous when unrecognized, however, if they can't be avoided or gotten rid of, they can usually be managed fairly easily.
Type Three Stupid people are so stupid they believe they are smart. They are so dense, they are incapable of realizing that 99% of humanity and 60% of Labrador Retrievers are smarter than they are. Impossible to deal with, but entertaining to watch... from a distance. Most of them have been identified for the village idiots they are and suitably contained, but there are a few who manage through nepotism or gross carelessness to occupy a position where they can wreak truly dangerous havoc. If they can't be avoided, don't even try to manage them, the only way to deal with them is to agree with everything they say and do - desperately resisting the temptation to inform them they are so full of shit - and as soon as possible, run, run away... far away.
*MENSA is supposed to be an association of the smartest people. In order to join you have to score in the 98th percentile on a 'normalized' IQ test (in other words picking the right A, B, C or D a hundred or so times), so that your raw score, whatever it was, is higher than the 97.99...% of fools who also took the test. There are no other qualifications to join MENSA, you don't need to be a qualified Rocket Surgeon or a Brain Scientist, or even demonstrate the ability to find your way out of a paper bag with both ends open (presumably MENSANs are good at chess or finding pi to the 200th decimal point, the Redneck has previously posted his thoughts about that). If you get the required score you get a membership card, and your name goes on the international MENSA member database. So what the Redneck wonders is, why would a highly intelligent person want the rest of the world to know they smarter than 97.99...% of the population if they were really all that smart? Didn't they read Kurt Vonnegut's short story, Harrison Bergeron???