Characters indicating that they are stylish by tying an onion to their belt.
- Rattlesnakes.
- Quicksand.
- Helicopters disappearing behind a hill before they explode.
- Cops chucking the lunch they just bought, and haven’t taken a bite of yet, out the car window when they suddenly get an emergency call.
- Nerds being the butt of jokes for dressing weird or having a weird laugh.
That’s a good one. And the TV punks always looked like no real street punk ever.
When dad’s boss comes to dinner so the whole family has to put in a big effort to impress him
One that crossed my mind a while back was ear blowing. Used to be when they showed a woman attempting to firt with/seduce a man (pretty much never the reverse) she would blow in his ear. But I can’t remember the last time I’ve noticed that being used.
I remember a bunch of family sitcoms in the 80s and 90s had the plot of a character wanted to break “a world record” so they would either try a single record all day but constantly be interrupted by other people, or try to do multiple records and fail every single one. Then at the end of the episode they would inevitably deus ex machina style still wind up getting a world record somehow, either “Most Attempts At A World Record in a Single Day” or some other accidental record like “Most falls from a pogo stick” if their record was trying to stay on a pogo stick for as long as possible.
I have no idea why they stopped doing that plotline, maybe because in the age of the internet nobody cares about useless world records to get themselves into the newspaper?
Another one that was used very often in old TV dramas-- a main character is in an accident and loses the ability to walk. At one point the person seems like they will succumb to sheer despair. But, through hard work and sheer determination, they finally regain the ability to walk! Usually within a single episode.
I’ve seen it in Bonanza and The Rifleman (Mark fell of his horse and couldn’t walk; at one point Lucas actually got a little mad at him for not trying hard enough to walk again. But by the end of the 1/2 hour, he was back on his feet). One of the Walton girls had several logs fall on her. I think it was a 2 or 3 episode arc before she could walk again.
Maybe I’m reading too much into it, but I’ve thought regarding that trope-- it seems insulting to real people who become paralyzed from an accident, can’t walk, and will never be able to walk again; suggesting if you just have enough determination and try hard enough, anybody can learn to walk again. So if you can’t in real life, you just didn’t try hard enough? Also kind of suggesting that if someone can’t walk, their lives are basically worthless.
So I’d say it’s a very good thing that this trope seems to have mostly gone away, though they did employ it recently in the Netflix Karate Kid sequel "Cobra Kai’.
The modern equivalent will probably become “trying to do something that will go viral on TikTok” 
How about the trope where male and female family members decide to reverse household roles, so the females end up doing all the repairs and the males end up cooking and cleaning (usually with disastrous results). This storyline seems to have vanished around the time the ERA failed to pass in the early 80’s.
Oh, yeah, good one, and it always ended happily, with each spouse having developed new respect for the other, having had no idea how difficult their spouses’ household roles actually were.
Temporarily, at least; the next episode would likely be a reversion to the mean.
And Hank Schrader in Breaking Bad.
Oh right, I completely forgot about that. Maybe I blocked it out of my memory because it was disappointing, an unfortunate old standard trope on a show that was normally great at avoiding or subverting tropes.
Bubbles. Sitcoms used to have a standard episode where someone uses too much soap and the house fills with suds.
Also, Mister Roberts
Both Dick Van Dyke and Sanford and Son used that one, in the 60s and 70s, respectively.
Women fainting, like when hearing bad news. Men standing up when a woman enters the room.
Pies in the face. Stylishly dressed gumshoe detectives. Guys smoking just to pass time.
This one also became less effective with the appearance of labor-saving devices and products. Today, Fred and Ricky would pop heat-and-eat foods into the microwave and have dinner ready in two minutes.
One trope I haven’t seen in a long time is Our Hero Gets Audited. This used to show up in 1960s-1970s sitcoms (Mary Tyler Moore’s character got audited, for instance). It gives you an opportunity to show Our Hero being exasperated by a circumstance people ought to be able to relate to, while using Screwy Ideas in moments of need (i.e. – writing a receipt out on a popsicle stick, since that’s all they had handy)
It fell out of favor because, I suspect, not that many people actually got audited, and those that did didn’t find it as much fun as A Barrel of Monkeys.
Another disappearing trope is Our Hero (or someone in the family) Gets Jury Duty.
Men pulling out a chair for a lady. (Except in old-timey shows of course).
Adjusting the TV antenna to get a better picture.
One I don’t think I’ve seen since I was a kid is the one where the characters go to a fancy restaurant, and discover the menu is written entirely in French. One character is too embarrassed to admit they can’t read French, so they just point to a random item on the menu. Everything here’s probably good anyway, they think. Inevitably, they end up ordering escargot. Or another variation is that the snooty waiter informs them that the words they’re pointing are in fact the dress code, or some other thing that’s isn’t an actual menu item.
I suspect this one got retired when chefs started branching out by the end of the 1980s, and fine dining establishments started serving things other than just French haute cuisine.