>In my (Admittedly limited) experience, there are four types of optimists. Three of these types are insufferable. Allow me to break them down.

Type #1 is the naive optimist. It seems only natural they would be optimists, because nothing bad has ever happened to them. They’re the transient optimists though, because it isn’t going to take much to shake them out of optimism, and when they crash and burn, it will be a real spectacle as they go down, unfortunately. I somewhat pity this type of optimist, because I know what’s in store for them. Most often seen in college freshmen.
Type #2 is the oblivious optimist. Sure, bad things happen to them. But Lemony Snicket captured this type of optimist perfectly, saying that: ‘If an optimist had his left arm chewed off by an alligator, he might say, in a pleasant and hopeful voice, “Well, this isn’t too bad. I don’t have my left arm anymore, but at least nobody will ever ask me whether I am right-handed or left-handed,” but most of us would say something more along the lines of “Aaaaah! My arm! My arm!”‘ This type is irritating, sure, mainly because their attempts to cheer you up are absolutely unhelpful and infuriating to boot. Think Igor saying, “Could be worse. Could be raining.” Most often seen in mild types who are somewhat selfless, but could be described as a bit of a cloud cuckoolander.
Type #3 is the worst optimist of all. It’s the “pearl clutching” optimist. Rather than blithely acknowledging the bad things, this optimist goes through every hoop possible to avoid the unpleasantness of life. If this optimist were a 19th century Russian novel, it would be The Death of Ivan Ilych. PCOs are hideously insecure, and often have some history of trauma from childhood that makes them terrified of unpleasant things, confrontation, or anything less than constant merry-sunshine happiness. These are the optimists who squeal at you to, “Oh my god, stop posting stories about the Congo, that’s so depressing!” These are the ones who can always cite sources on how happiness helps people live longer, but are unwilling to scratch the surface and wonder why it is some groups are more “happy” than others, and the role that oppression plays in determining one’s happiness. PCOs are, at their very core, selfish. Their optimism stems from a sheer willingness to ignore the unhappiness of everyone else in order to ensure their own. Most often seen in cowards, that one person who runs away or starts trying laughably ineffective ways to stop a minor squabble, or that one friend who says zie’s too busy to worry about the world.
And finally, Type #4 is the one optimist whom I can happily spend time around. This optimist is no stranger to agony, either that of hir own experience or others. Rather than trying to run away from it, ignore it, or gloss over it though, Type #4, the survivor optimist, acknowledges that pain and suffering, and asks, “What can I do to alleviate this?” or “How can I make sure that nobody ever goes through what I did?” Survivor optimists are aware of the never ending battle that awaits them, and what the stakes are for their cause. But they keep at it, because they care so deeply about it. Even when it seems like all is lost, the survivor optimist holds out. What distinguishes this optimist is that they don’t passively wait for things to get better. Their hands and hearts are dirty with their dedication to righting wrongs.
Most often seen in activists, progressive bloggers, advocates, volunteers, and their ilk.