It’s just a term for describing disliking hearing people smack their lips. I’m not claiming it’s a disease or disability.

It is different than just a simple “dislike”. I can’t really explain it, but hearing mouth noises (chewing, swallowing, lip smacking) invokes deep, almost instinctual anger within me. I can’t explain it, but it is certainly different.

This is a very real thing. I dated someone who went through the roof when she could hear any mouth sounds, even dogs licking their coats.

"I haven't heard of this thing before so it sounds made up"

Oof, as someone that suffers from moderate misophonia, I can assure you it is real and how lucky you are to have not heard of it. It can be torturous, and I don't even have it that bad.

There's a subreddit with 62k members if you're curious https://www.reddit.com/r/misophonia

If it "sounds made up" to you, then you won't mind if I come and stand behind you when you're trying to work and squeak a block of polystyrene up and down the window.

The reality is that it's just a fancy name for people/things that sound annoying, and if you're forced to hear it for long periods of time, one day you might find it extremely more annoying to the point where you have to say something or walk away, usually coinciding with some other stress.

Remember the Simpsons episode where Homer's nose whistling was what finally made Flanders snap?

Whether it's a serious AND common AND acute disorder is up for debate. In the early/mid-2000's a fire started smoldering on the Internet regarding wanting to find a clinical jargony label for every aspect of life, and Wikipedia turned it into a wildfire.