Nothing in the world irritates me more than a closed-minded individual. These people see their way of thinking as the only RIGHT way of thinking, and refuse to open up to new ideas, or the possibility that, Heaven forbid, they just MIGHT be wrong about something. I encounter people like this every day in school, on the street, on line, or even while playing someof my favorite games. They'll get into a "discussion" with you about what they believe, and why you should see, think, do, etc. things the way that they do, but will not budge if you provide a counterpoint to their egocentric ways of thinking. If you even DARE to try to prove them wrong, or hint that their reasoning is faulty, they'll often go ballistic, and either start screaming at you, calling you a liar, or just close up altogether, and refuse to listen anymore (of course you're wrong, so they don't have to listen to a word that you say, anyway). Some of the most closed-minded people that I have encountered in life are the "devoutly" religious people who see everything in either black or white, with not a shade of grey in between. They go through life with their blinders on, so focused on their own beliefs, and what is being fed to them, that no other possible viewpoint will be accepted, no matter what real value those viewpoints hold. My mother, bless her soul, is one of these people. Don't get me wrong, because I do love her dearly, but I try very hard to avoid any discussion regarding politics or religion with her, because I know that, no matter how I try to point out her often faulty reasoning, she will stand her ground and tell me how wrong I am. I also have encountered people that I had considered to be friends in other forums as well. These people had developed the mindset that what they wanted was exactly what everyone else wanted, and when they were confronted about it, and told "this is NOT what everyone wants, and therefore, you are NOT meeting the desires and needs of everyone else." they immediately went on the defensive, calling those who opposed their thinking liars and "disruptive influences" and immediately silenced them and their ideas by excommunication (ie. blocking access to any forum that THEY controlled, etc. just to prevent the disease of "wrong-thinking" from spreading to anyone else.) They didn't stop there, either. To further cement their beliefs, and maintain their "control" over people, they fabricated lies about those who opposed them, and proceded to turn others against the opposition. This is where closed-mindedness begins to become dangerous.
Closed-minded individuals often develop extreme prejudices toward certain races, ethnic groups, religions, and other ways of life. Infamous people that come to mind are Adolf Hitler (lets exterminate the Jews, their sypathisers and anyone else that doesn't match my ideals of 'perfection') and- more recently- the Reverend Fred Phelps and his flock of sheep, er followers, from the Westboro Baptist Church (whose hatred is broader and often more violent (let's protest gays, gay rights, blacks, democrats, islam, or -insert other things that 'God hates' here.) People like this are dangerous, and make me wary of poking my head outside my door lest they find something that I believe in wrong or "evil" and violently beat or kill me for.
Unfortunately, closed-minded people can rarely be persuaded to change their ways of thinking, and must be tolerated. As for myself, I prefer to keep my mind open to new ideas and possibilities. In my opinion, that's the only way to grow intellectually as a person. Like the saying goes, "A mind is like a parachute, it functions best when open."