The sexy shower for two.
Couple laying on the beach and the ocean tide comes in.
Bathtub/hottub funzies night.
I’m afraid water sex might be…ummm…not as much as it’s cracked up to be.
A line from WC Fields comes to mind… 
If a big fancy cake is shown (such as a wedding cake) it will be smashed. Usually by someones face.
If there is a big build up to a wedding- something will go wrong.
If a middle-aged man says he’s having “a spot of indigestion” at the dinner table, he’ll be dead of a heart attack by the time dessert is served.
This is a corollary of the “two coughs” rule referenced above.
My contribution:
Any abrasion or cut to the face on the star will require, at most, two butterfly bandages - never stitches.
Nosebleeds are a dead giveaway that someone has telekinetic powers.
Any woman who vomits or is nauseated is pregnant.
In a period piece, anyone who coughs more than once will die of consumption.
Roger Ebert dubbed this the “Law of Evil Marksmanship.”
Nitpick: The Principle of Evil Marksmanship, according to all the references I could find online (like Roger Ebert's Little Movie Glossary or The Roger Ebert Glossary of Movie Terms).
Sorry, my copy of the former has been in storage for several years. I was working from memory.
And when you come across the danger on that road and hit either the gas or the brakes fast, your tires will somehow squeal on that loose gravel.
And that cat will inevitably yowl loudly just to bring home the point that it’s a cat.
Also, if the good guy does get hit by a bad guy’s bullet, it’ll be in either the leg or the shoulder, and he’ll be fine, aside from maybe wearing a sling or using just one crutch, because it’s not like there are a lot of important blood vessels in those areas.
Movie characters can also tell immediately if a crime victim is dead. They know when there’s no point in trying to resuscitate a person on the ground or even try to find vital signs. They wouldn’t want to contaminate the crime scene, after all.
Why when danger of a psychotic maniac is approaching do the scared cabin dwellers run towards the forest and not get in the car and speed away? Everytime.
A villain who abandons his evil ways and redeems himself by doing something good, (depending, to some extent, on the depths of his previous evil) has the life expectancy of a mayfly.
Perhaps the only character with a higher mortality rate than the one who coughed a couple of times.
Any group of co-workers who are working late will be shown eating Chinese food out of the container with chopsticks.
mmm
This is one of the reasons why Evil Dead is such a great film. The characters actually make inteligent choices and act reasonably. It doesn’t help them at all. But, it makes for a great film.
Known as “Chekhov’s Wedding Cake”
Ha! I was thinking the same thing.
When I saw the movie Everything Everywhere All at Once I took the gilded “Buttplug” awards on Jamie Lee Curtis’ desk as a satirical comment.
It wasn’t until later that I learned, to my chagrin, that they were Chekhov’s Butt Plugs, and therefore had to be shown to be used by the third act.
Thank Og for pixellation.
TV Tropes calls it Imperial Stormtrooper Marksmanship, and has several examples of it in several media.
A few corollaries of my own:
If a young woman throws up, she’s pregnant (unless a central plot point is that she’s hung over).
If a lone person is shown driving for more than a second or two, especially a closeup shot lingering on their face, they’re about to get in a terrible traffic accident.
Not so much corollary as agreement with addendum: if the reformed bad guy has done something irredeemable, like having killed a good guy, their only possible best outcome is to die a ‘good death’ while doing something that helps the good guys succeed.
Some tropes are so well-established that TV and movie writers have gotten good at manipulating them to fake out expectations and tease the audience. Vince Gilligan and his writers were masters of that in ‘Breaking Bad’ and ‘Better Call Saul’.