The following excerpt is from a post on Brute Reason discussing the problems with using psychiatric terms in a colloquial and metaphorical sense.
These words are used so casually that our conception of their meaning gradually shifts without our even noticing it. It’s like a boy-who-cried-wolf type of situation in that regard. If nine different friends joke to you about how they’re ‘sooooo OCD’ because they like all their books organized just so on their shelf (a situation familiar to just about every bibliophile, honestly), then the tenth friend who comes to you and tells you that they have OCD is probably going to evoke that mental image, rather than one of someone who actually can’t stop obsessing over particular little things and carrying out rituals that interfere with that person’s normal functioning, perhaps to the point of triggering comorbid disorders like depression. This may be a person who washes their hands until they are raw and hurting, someone who has to flick the light switch on and off seven times every time they leave a room, or someone who has recurring, uncontrollable thoughts about hurting someone they love even though they have no actual desire to do that.Well, that sounds a little different than insisting that your books be categorized by subject and then alphabetized by author, no?Likewise, if your friends are constantly telling you they’re ‘depressed’ because their team lost or because they got a bad grade, only to return to their normal, cheerful selves within a few hours, the next person who tells you that they are “depressed” might elicit a reaction of, ‘Come on, get over it! You’ll feel better if you go out with us.’
And so the meanings of words change.