People living in space will have every high-tech device imaginable, and dress in super spandex and super lycra. People who live on colony worlds, which presumably will have some fairly advanced tech, too, will for some reason live in mud and wattle homes, dress in rags, and use ancient tech for the most part. (Firefly fans, I’m looking at you, but there’s plenty of others (Star Trek, Star Wars, Riddick, etc.) that go for this, too.
Funny. If I look a couple thousand miles to the southwest I see some nations where stuff like that isn’t unusual. If I go a few thousand more to the southeast I find the same thing.
What was your point?
-Joe
Although a submarine about the length of Serenity, but narrower, can carry enough canned goods to feed a crew of, say, 180 for several months while it’s submerged, once you’re in space then a crew of eight is pretty much stuck eating food cubes and reconstituted protein mush during a trip that will take a couple of weeks.
Corollary: What little clothing women do wear must include a brass bra.
There are actually humans living all over the galaxy, having been kidnapped by aliens and relocated to distant worlds – usually they have either been abandoned or have overthrown their oppressors.
Energy bolts from handheld energy weapons (phasers, lasers, ray guns) travel slower than bullets from handguns, and they can often be dodged by their targets.
Now I know that Jim is actually your name but it made this post so much funnier.
Reversing the Polarity of your device allowsw you to undo any bad stuff.
Time Travel paradoxes are unaffected by logic
We don’t need no stinking Relativity!
All sorts of ray guns are visible from the side, even without any scattering medium.
Alien cultures, although they might differ in language and other details, are really more familiar to you and easier to come to terms with than another human culture from the other side of your globe.
Women traveling through outer space not only wear makeup, but apparently take the time to apply fresh makeup between battles/alien encounters/sleeping periods. Going for a space walk, girls? Grab that mascara!
All worlds have homogenous climates, cultures, languages and landscapes.
Any religion as it is practised on its homeworld will inevitably have a negative impact on you.
You have to get the enemy in visual range in order to shoot at them.
One hit, and the enemy fighter is always destroyed. Your fighters, OTOH, can withstand hits just long enough to ram into another enemy ship and destroy it, freeing the hero.
Aliens come in two varieties: 1. mindlessly evil, or 2. almost godlike in their goodness. Those that actually appear godlike are really mindlessly evil.
A cure for any disease can be found within a week. If it’s an alien disease, five days.
Explosions in space make noise.
You can find planet that are exactly like Earth, except that one event from our history happened differently, creating a completely different culture.
No matter how big the ship (and supply of air in it), you will die in less than an hour if life support fails.
Alien women look as good, if not better, than human women.
The humanoid form is the form of all intelligent beings in the universe. You can only tell the difference due to bumps on their heads. (There must be a big deman for phrenologists in the future).
No matter how superintelligent a computer is, you can defeat it with a simple logical paradox (“Everything I say is a lie”).
The last couple alive after an atomic holocaust will be named “Adam” and “Eve.”
The “crackpot” scientist who warns you about the dangers of what you’re doing will turn out to be right.
I learned that from reading the newspaper these past few weeks…
You never watched Junkyard Wars, did you?
Not only that, but viruses from Macs will run on alien computers, even though they won’t run on Windows or Linux/Unix machines on earth.
All planets have one ecosystem (desert, ice, jungle, etc) and one culture.
Hybrids of two alien species never have any health or mental problems as a result.
If you blow up a comet just before it hits the Earth, that will somehow make things all right. Never mind that all of the mass of the comet is still hitting the Earth but is more spread out, which would probably actually make things worse rather than better.
There are previously undiscovered asteroids the size of Texas, on Earth-crossing orbits, in the solar system.
The Sirius Cybernetics Corporation:Proudly supplying Starfleet with transporters and replicators since 2213.
Alien languages frequently use silent apostrophes as both vowells and cosonants.
Of course you can, but I learned it first from Spock & Scotty. 
PookahMacPhellimey 
I’m a Doctor **Jim ** not a bricklayer.
Jim
On a planet named “Bean” the planetary capital will be called “Beanopolis,” the language will be “Beanish”–etc. And the drug that saves the day will be called [no, can’t do it]
On a newly discovered planet, there’s always a secret. It’s not enough that it’s a different culture and biosphere, oh no, that would be too easy. They eat their young or they’re gonna eat you or something.
Finding a cure for the alien disease means that you’ll be healed in minutes, with no aftereffects. Scars disappear, arms grow back, sight returns to the blind. And there are never any side-effects in the future either. No “some users report itching, swelling or diarrhea” sort of thing.
Well… side-track, but I never really got the idea that the drab diet on Serenity was due to lack of space… just financial concerns, (ie, the cheapest thing available, or something like that.) Also, how science-fiction-y would it be to have them eating canned carrots?
Oh, and crew members never bring back communicable alien diseases from a planet to the ship. This is true even when they visit a planet where one or more members of the crew are capable of interbreeding with the natives, or where the natives are the same species as one of the crew members. Or else there is some way for the transporter to filter out the potentially harmful viruses/bacteria without affecting the body’s beneficial bacteria. This filter works perfectly for all species in the crew, including hybrids.
Interstellar spaceships never transmit communicable alien diseases to planets they visit, either, unlike the Europeans when they first visited the New World. This is true even when the natives of a planet are the same species as one of the crew, or able to interbreed with at least one of the crew, and no matter what technology the natives do or don’t have to prevent and treat disease.
Superior ability creates superior ambition. We must therefore be imagining all those intelligent slackers that we know.
Or tinfoil underpants. Or is that just the slave girls?
I once read a hilarious parody online about a “transporter” system that consisted of freezing people solid, slicing them into cubes, sending the cubes in the mail to their destination, gluing the cubes back together and then recescitating the person.
After an atomic war or radiation accident, all mutations will be either horrid monsters of geniuses (sometimes evil.) All mutations will be of the same type.
All planets will have exactly one type of climate - ice or desert or forest.
(1940s style) - All asteroids have breathable atmospheres.
Asteroids in asteroid belts are all about 100 feet apart, of a nice uniform size, and travel in just a way that a hot spaceship pilot can go through them.
Rocky Jones - when you shoot a spaceship with your weapon, in space, it falls down.
No matter how old the Galaxy, any races we meet will either be at our technological level, or be godlike and not care about us, or be ancient and stagnant, just waitng for us to put them right.
…As well as a lot of X’s K’s and Z’s.
Or, you can simply destroy its monitor. Computers explode and catch fire if their monitors are damaged.
As long as they’re blue.