Since I've been too busy this month to come up with any whacky machines or deranged schemes, I've instead decided to tell you about how fiction depicts science badly in ways that inevitably lead to my friends asking me stupid questions. Note that things required to the plot are acceptable breaks from reality, because a space opera that has 450 year breaks in the action would be unwatchably boring.
* Beings "Made of energy."
Energy is not a thing. Energy is a trait that things have. A "collection of energy" would not be able to have the required structure to maintain life. While this error is popular because energy is "intangible," leaving your heroes with the frightening prospect of an opponent able to walk through walls and such, it is unspeakably stupid. Also the usual solution of stuffing them into a battery or otherwise utilizing their component energy to destroy them demonstrates a certain lack of respect for...fact.
Or on the flip side of this, matter is interchangeable for energy, so I am "Made of pure energy" too, as are you. Therefore making this idea equally stupid.
* Being from "the beginning of time" and "the end of time."
While this came up to make the monster-of-the-week sound more fearsome, the truth is the opposite. A being from the beginning of time would lack complexity, due to a lack of available materials. There's not much you can do with just hydrogen. A being from "The end of time," which I take to mean the heat death of the universe, would have little energy available to it, and therefore would have to be geared more towards conserving this energy than intelligence, combat initiative, or whatever else the writer seemed to think it would develop. Superhuman intelligence and combat reflexes aren't going to do you much good if you starve to death, ya know?
* Aliens that are preoccupied with humans
This just smacks of collective egotism. If an alien did encounter the Earth, there's no reason why it would find us special automatically. In fact, an alien finding the earth might easily get distracted by the oceans, which cover 70% of the planet, conclude that the earth was a dull ocean world, and leave.
* Nuclear = OMG DANGEROUS
If nuclear, "atomic", or radioactive substances appear in the show, they will almost always be dealt with in a hysterical manner, assuming that all of these substances are made of pure evil and will cause anyone that so much as looks at them to die.
Likewise, assuming something is dangerous because it is "atomic." Everything that can be handled has atoms. They are not dangerous.
Radiation is a danger, because it burns biological life, the same way a hot stove does. But if you're afraid of your hot stove, there is something wrong with you. Radiation can be dealt with, there are engineering things that can be done to lessen or eliminate the dangers.
This was more common in productions made in the 1950s, and is mostly giving way to:
* Genetic Engineering = Evil
A genetically engineered or cloned organism is almost always depicted as being an uncontrollable monster that hungers for human flesh. Likewise, humans who are genetically engineered or cloned are unemotional, perfectly willing to follow orders, and evil.
Genes do not do this. Genes determine how an organism will produce proteins, which in turn determine the organism's shape and physical traits. There are genes for blue eyes, there is no gene for "evil."
The biggest real threat in genetic engineering is allergies. For instance, some tomatoes are genetically engineered with fish genes to make them ripen sooner. People that are allergic to fish are also allergic to these tomatoes, because the proteins resemble the fish proteins that their bodies are oversensitive to.
Another worry is that genetically engineered plants will cross pollinate natural plants. This would not be a big deal, except that A) the genetic engineering companies regard this as copyright violation and sue, and B) the genetic engineering companies often insert genes into the organisms they make to make them sterile. Large swaths of plants going sterile, and the farmers who grow them abruptly getting nonsensical lawsuits is a big problem.
* Outright unit errors
Watts is energy over time, or "power" as physicists understand the term. Volts measure electrical force. Ohms measure resistance. Light years are distance. Amps are number of electrons.
Even George Lucas messed this up and had to severely retcon himself. ("I did the Kessel Run in 6 parsecs." He then had to make up a story about the Kessel Run involving many black holes to cover up the fact that he thought Parsec was a unit of time, when it is actually distance.)
* Silly rules
The reactor only works when operated by a Hindu born in Mumbai. This is not explained away with a security based explanation, (which might actually make sense if the station was built by Mumbaians who wanted to thumb their nose at everyone else, and had some way of actually detecting the religion of the person operating it,) but with techno babble. Again, a blatant "this group is special" effect appears, stinking up the whole script.
* Likewise, biology non-sequiturs
Vitalism is false, but I can't tell you how often I've seen a script where getting a resource cruelly from a biological source oddly counts more than from mechanical ones. For instance, a sugar reactor magically (and illogically) getting more energy out of blood than from bags of sucrose, despite blood containing less than 1% sugar by volume.
* Destroy the Earth
"You can't spray that can, it'll destroy the earth!" Usually, they mean destroy all life on earth, which is much easier to do. Actually destroying the earth is very very very difficult.
A meteor that would destroy all life on earth would be about 3 miles wide. A meteor that would destroy the earth would be larger than the moon.
Holy cheese, there's more wrong with fictional robots than I have space in one entry for, so I'm breaking it up
* Robots hate Biological Beings
For some reason, all Robots, Computers, AIs, and other technology-based entities are depicted with a deranged hatred of any human, animal, or other biological based being. Who the hell programmed them that way? Since computers are programmed and follow their programming literally, this leads to the ridiculous conclusion that all the available programmers were severe nihilists who both wanted to commit suicide and take all biological life with them.
* Illogical instructions equals explosion
Because clearly surge protectors don't exist. A computer confronted with invalid instructions tends to lock up, crash, or reboot, not explode.
* That is illogical
Robots in fiction seem to have this supernatural ability to grasp the truth of the matter and scorn any attempts to deceive.
The truth of the matter is, as computer science majors say, "Garbage in, Garbage Out." If you tell a computer that Pi is 5, it will blithely run with it, producing all kinds of odd, illogical results. If you tell it that you are 600 feet tall, and ask it your weight, it will probably give an answer around 1900 - 2200 pounds.
For all my hatred of these, I see them constantly. They grate me the way that spelling, pronunciation, or grammar errors would grate an English major. Argh.