- Any number of fad toys. The '80s had Cabbage Patch Kids, (which lasted through The '90s and are making a valiant attempt at a resurgence), Teddy Ruxpin, Simon, pocket games that play only one game (such as Pac-Man or Centipede), Pound Puppies, the Snoopy snow cone maker, and Rainbow Brite (though those last three are making something of a comeback). In The '90s, it was Tamagotchi note , Tickle-Me-Elmo, Beanie Babies, pogs ("tazos" in Mexico, Australia and other countries)... the list is ever-growing. Anyone who grew up at the time that any one of these were popular has probably witnessed the popularity arc go from "niche item that only a few people have heard of" to "waiting in line for half a day just to get one, then seeing people fight in the store over the remaining stock" to "finding a bunch of well-worn ones for 50 cents at Goodwill".
- For the old fogies in the crowd: Pet rocks. Mood rings. Lava lamps. (Although that last one has never quite gone entirely away, but is now mostly the venue of young kids and people of a certain age who buy them for either camp or nostalgia. A lava lamp seen in a movie or TV show is an indicator that its owner smokes a lot of pot.)
- Once upon a time, any Fantasy, Science Fiction, or Action Adventure movie or TV series would get a short lived toyline. Planet of the Apes, The Six Million Dollar Man, Logan's Run, Star Wars (which is still going strong), Star Trek, Raiders of the Lost Ark, Space: 1999, Battlestar Galactica, Buck Rogers in the 25th Century, The A-Team, Dukes Of Hazzard, The Munsters, The Addams Family, Smokey and the Bandit, Cannonball Run, CHiPs, and Knight Rider all had toylines. Even seemingly unlikely candidates such as Ralph Bakshi's The Lord of the Rings, the R-rated Alien, Blade Runner, and Rambo or even the PG-13–rated 1984 Dune had toys produced. There was also TV tie-in toy merchandising with mainstream shows like Bonanza, All in the Family, Welcome Back, Kotter, The Brady Bunch and M*A*S*H. Most of these are still collectible today. What is worth remembering at the time is that these toys were targeted toward children and not toward adult geeks. This makes it amazing that they created toy-lines based on films that children were not likely allowed to watch, such as the aforementioned R-rated films. Don't look for any toylines based on most of today's genre shows or films, there will definitely be no more tie-ins toy-lines for for Prime Time television comedies or shows. Today's trend is towards more naturalistic settings and characters in genre films and series, and a good number of them are strictly adult level and not suitable for viewing by children. At the very least, children may be bored by the lack of action. The current trend in genre shows is slow paced episodic stories that focus on character melodrama, so making action figures for the majority of these shows (such as Game of Thrones, Sherlock or Penny Dreadful) is somewhat absurd. In the rare occurrences that such toys are made today, an immediate backlash is inevitable, the toys (actually available at Toys R Us) based on Breaking Bad being a perfect example. These toys were immediately pulled from the store shelves.
- Home chemistry sets and other science kits, thanks to a combination of perceived dangers to life and limb and the Wars on Terror and Drugs. The Gabriel and Skillcraft sets were highly acclaimed for being equipped with everything a budding young chemist needs: scaled-down chemical glassware (real Pyrex), apparatus, and a host of chemicals used by real chemists. As a bonus, you could order from their catalogs for even more items. However, due to perceived safety concerns and fear of lawsuits from angry parents, test tubes and beakers are now plastic; there are no alcohol burners; chemicals are now mostly limited to vinegar, table salt, table sugar, and other "safe" household items that are expected to already be on hand, and experiments are limited to simple, boring reactions such as color changes.
On top of that, there is a fear among police and various public safety groups and advocates that chemistry sets can be used to manufacture explosives and methamphetamines. (Breaking Bad has likely done little to help with the latter image.) Thanks to this, there have been a number of highly publicized police raids into the homes of what were nothing more than chemistry hobbyists, and suppliers became very leery about selling their products to anybody other than schools and laboratories. Some states, such as Texas, have even gone as far as requiring a government permit for the possession of just chemistry glassware.
- Cartoon/toy-line tie-ins: These are now considered strictly a relic of The '80s. Transformers, G.I. Joe, Voltron, Masters of the Universe, and many others had popular cartoon shows that were arguably just advertisements for the toylines. Strict government regulations against child-targeted commercial advertising saw the end of this sort of marketing. Today, toys based on these older franchises are targeted toward nostalgic adults and are priced accordingly. Transformers, however, seems to have survived and is still going strong.
- Any toys that resemble real-life firearms or weapons. Drug and/or gang wars of The '80s and onward involved a lot of gun-play, and city kids who brandished realistic fake weapons risked being shot for real by criminals, police officers, or both. To safeguard kids, toy guns now are brightly colored (black is disappearing), usually have a tell-all orange tip barrel, represent no commonly available firearms, and can't be easily painted to resemble real guns — they look more like fantasy / Sci-Fi weapons. Also thanks to this law, the original Transformers toy of Megatron cannot be reissued in the US. Usually, their appearance is also out of proportion with real guns so they can be spotted at first glance. Cap guns, meanwhile, have vanished due to the public's tendency to mistake their noise for real gunshots. Water guns like Super Soakers, however, are still very popular, largely because nobody could confuse them for real guns.
- The only "toy" guns still sold today that resemble real weapons are BB rifles, which get by on the Grandfather Clause (the Daisy Red Ryder BB gun was famously featured in A Christmas Story, after all), and Airsoft guns, which are often very expensive and marketed strictly to hobbyists and the like. And even in those cases, nearly half of all US states regulate their sale and use.
- Toy soldiers based on any historical war. Back in the days of World War II, the US Military were undoubtedly the rough 'n' ready good guys fighting valiantly for liberty and justice against the evil Nazi Germany regime. With the onset of The Vietnam War and especially The War on Terror, we began seeing more shades of gray, such as innocent people on "the other side" suffering as a result of the wars, the American Government making some objectively boneheaded decisions, and fathers who served in the wars either dying or coming home crippled. It more-or-less became clear that War Is Hell and not the kind of thing we want our kids glorifying.
- This can be seen easily with G.I. Joe. The original figures were explicitly designed as American infantrymen, but after Vietnam, the line shifted focus to adventure stories or battling absurd supervillains, largely jettisoning anything that could associated with an actual war. It's hard to imagine, for instance, Snake-Eyes in Afghanistan.
- Bratz dolls. When they first came out at the Turn of the Millennium, the fashion dolls were hugely popular in a way no prior Barbie rival had ever been, and very controversial due to their "slutty" appearance for characters who were supposed to be teenagers. Now thanks to said controversy dying out, several failed retools and spinoffs, a lengthy hiatus due to legal issues, and the rise of doll lines such as Monster High that feature Loads and Loads of Characters with truly distinctive personalities and strong World Building, the Bratz franchise is struggling to stay afloat and is virtually dead. There's a good chance most toy-buying kids aren't aware the line still exists, or even existed. A reboot of the line came along in 2015 but many, even former fans, doubt it will last long.
- Even Moxie Girlz, created by the same company to replace it, isn't doing too well and now exists mainly as a Lighter and Softer budget line.
- Sea Monkeys was one of those "hard to believe it was popular" fads. Inspired by ant farms, these were homegrown brine shrimp marketed as novelty aquarium pets, heavily marketed, especially in comic books starting in 1957. Unfortunately, the advertising was rather deceptive, showing humanoid animals that bore no real resemblance to the actual shrimp, and many buyers were disappointed by the dissimilarity and by the short lifespan of the animals, and the fad eventually died out. Although, Sea Monkeys had one moment of glory in 1998, when astronaut John Glenn took some aboard Space Shuttle Discovery during mission STS-95. After nine days in space, they were returned to Earth, and hatched eight weeks later apparently unaffected by their travels.
- LJN Toys used to be up there with Mattel. Now they are mostly remembered for two things, abysmal licensed games, and The Angry Video Game Nerd trashing said games. The company's swan song was in 1995, when Acclaim (which itself became Deader Than Disco), which acquired LJN in 1990, retired the LJN brand name (except for a short 2000 revival).
- Among Transformers fans, frenzy_rumble was a popular customizer who made everything into a Combining Mecha. The desire to get updates of classic combiners and new ones (such as turning perennial Ensemble Darkhorses Dinobots into a combiner got him a lot of praise. However, the fandom soon grew tired of the perceived laziness of his designs (that they were essentially Transformers bolted onto an existing skeleton, rather than turning into the limbs themselves) and rumors of stealing ideas and not following through on commissions didn't help. Finally, the third-party boom completely put him to rest. Suddenly companies making better combiners made him obsolete.
Deader Than Disco / Toys
If there's anything parents know, it's how kids obsess over the latest thing, then forget about it after a week or so, hence why the Trend Aesop exists.