Regarding the movie Waiting, while there's definitely some truth to the movie, in my experience, it's extremely exaggerated for effect.
I worked in that industry for years at more than half a dozen restaurants, from major chains to small nationally-acclaimed restaurants to high-end spots where the service staff wore dinner jackets and ties. Obviously I know a lot of people in the industry too.
And I've personally never seen anyone actually mess with the food, nor do I recall hearing of anyone messing with food. Now, there are certainly times when the food is less than fresh, and in general, the quality of ingredients at many chains is barely even real food.
But again, tampering with food is much more rare, and it's certainly not done right in the middle of the kitchen.
A few things to keep in mind:
1. If you don't like anything about your food or your experience in the restaurant, the waiter doesn't get paid -- or gets paid less. This is why, first and foremost, you should be decent to your waiter.
2. If there's something wrong with your food, the manager has to go out and deal with it, which usually includes some form of grovelling, comping items, etc. Most managers have no desire to deal with angry customers on a regular basis, and they don't want to deal with wasted food either.
3. If there's something wrong with your food, the cooks have to remake it. This is just more hassle for them.
4. There are people in and out of the kitchen constantly. Either everyone would have to be in on the food tampering, including waiters, cooks, and managers, or it only takes one of those people (or cameras) to see it happening and make it an issue.
While most people working in restaurants dislike their jobs, they typically want to avoid: 1) getting fired; and, 2) making more work for themselves. Even in the shittier restaurants I worked at, most of the staff had been there for years.
Basically the "joke" of Waiting is that it's just an absolutely terrible restaurant, where everyone is the worst exaggeration of restaurant staff possible. Again, there are definitely elements of truth, but it's really cranked up to 11 and 90% of that stuff doesn't actually happen like that. For example, them showing each other their balls was a much exaggerated version of the "Circle Game", where you get someone to look at your hand when it's below your waist.
On the other hand, I have no doubt that it happens in fast food chains. Because the pay is lower, the job requirements are lower, there's less supervision, etc. That's where you find the real low down degenerates, like Cr33pin.
With all that said, I would not personally eat at places like Applebee's, because the food is just overpriced trash. And I can't stand Starbucks, which is also overpriced trash. And lastly, the "woke" crowd is so insane that I wouldn't put anything past them.
However, in my experience, I don't remember much progressive nonsense when I worked in restaurants. I'm sure plenty of them were liberals, but it didn't really come up much. Also, waiters tend to be racist because black (and Asian and Indian) people don't tip.