There are too many of them and not enough of you. Also, idiocy is typically a temporary condition for most people.
The basic concept to take away from this post is don't talk/email/interact with people when you are out of sorts and/or out of control. I know, way easier to say than to do (but hard to type, what with all the slashes (/).
Also, use your eyes, ears, and gut to notice things like major mood swing issues with others. People who are angry or upset are clenched up; rarely are they relaxed in demeanor. Some get very quiet, others get very shrill. You can tell after talking to someone a few minutes that maybe they're not at their best.
Recommendation: walk away.
You don't want them killing you for being an idiot, either.
This is all pretty basic advice: most people know not to poke the angry beast when the angry beast is being angry. Which is why noticing when you are the angry beast--the first part of this blog post--is a skill to hone.
Get grumpy when you don't eat or don't get that first cup of coffee? Don't talk to people about controversial subjects (or at all if you can avoid it), until those hurdles have been leaped. Low blood sugar and caffeine addiction are reasons for bad behavior; they do not erase it or excuse it. If a co-worker felt the need to blast your head off for saying "Good morning," to him or her, you're probably not going to feel charitable towards them if your head could have remained in place had they but eaten their breakfast bar.
A lot of issues regarding anger/fear/anxiety/upset in the work place are specific to physical conditions of the body. You could be really tired, really hungry, crashing from sugar, jonesing for caffeine, or if you're particularly a braniac, you could be recovering from a hangover. All of these are conditions that have been brought on by yourself, the same way that a driver who loses control of a car because of a faulty tire is to blame: it's the driver's JOB to make sure the vehicle is safe to operate, and its your job to make sure you are safe to be around other people.
Now you may have a baby at home, which is what is killing your ability to sleep; you could blame the baby for your lack of sleep, or your wife for sleeping because it was your turn to cope with baby last night. However, its not really anyone's fault here: you made a choice to participate in the raising of a beautiful, awesome creature that hasn't figured out the concept of a schedule yet. Your co-workers did not get consulted about that. First, that would be weird, and second, they don't expect to be. But they do expect you to perform as well as you did before the kid came along, with a few exceptions because they are not heartless automatons, and some of them probably have kids, too.
So if you're prone to bouts of unreasonableness when you're tired, they will put up with a bit of it--kids are awesome and they are a lot of work--but you never want to push them too far on that. This may mean mini-naps at lunchtime for you, or napping instead of your normal decompression when you get home (when you can, as baby and family life permits). This may mean--if you aren't nursing--consuming more caffeine than you might otherwise to keep the peace.
Whatever you do, be AWARE. You may need to make a note for yourself related to physical conditions and keep it on your monitor or tacked to your phone to remind you that the guy you're talking to on the phone might not actually be a moron, it might be that you're in a bit of a pissy mood. Also, regardless of mood, never treat anyone like a complete moron. You might be right, but the workplace rarely rewards people for calling out complete morons. Someone had to hire that moron. They might not enjoy you pointing out their mistake.
The second big reason you could try/want to kill the idiots is mood related to emotional context. You come into work having narrowly avoided an accident caused by someone talking on their cell, then run into a co-worker talking on his cell, there is a temptation to lash out. Needless to say, DON'T. Easy to say, by the way. Hard to realize that you might be in an altered state due to emotional issues going on.
Have a sick kid at home? Buying a house? Managing a promotion? Comforting a friend whose loved one has died? These all eat up energy from you. The less energy you have, the more likely you are to turn evil at a moment's notice.
So, question what comes out of your mouth, before it comes out of your mouth. Is it polite? Is it emotional? If its emotional, where is the emotion coming from? Note, some people NEVER MASTER THIS SKILL. There is a disconnect between their ability to filter and their brain. Many of them are hilarious. Many of them are never going to get terribly far, depending on their career of choice.
In summary, question yourself before you question other people. Preferably in your head. Despite Gizmodo's recent article about talking to yourself making you smarter (and not actually crazy), many people are still hung up on the crazy part. Also, unfiltered external dialog is a lot like leaving TNT lying around for the cat to play with: generally a bad idea. You never know who will over hear you. You also don't know who the person you are talking to today will be tomorrow; a simple kindness (such as rushing for coffee before having a quick morning discussion), could make or break someone's impression of you, and those impressions have long lives in the increasingly cozy career world where someone who was your co-worker yesterday is your boss tomorrow.