These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Americans Hate Tingle: The game is popular everywhere, except in Mexico, the native land of the programmers. In fact, Mexican videogame press barely, if even, talked about the game and the few Mexican players who played the game thought it was another American or European game. It doesn't help the homepage is in English, without any Spanish-language version of the page and the game itself is in English.
Awesome Music: The soundtrack is pretty good overall, but the tune that plays in the Research and Development center is just the perfect tune to get one psyched up for a space flight. It sounds like something you would hear on a movie about space flights.
The tune played when you break out of atmosphere is haunting and 2001-esque.
Internet Backdraft: The community is generally a pretty laid-back bunch, but there are two particular topics that tend to be the subject of intense debate whenever they're brought up: Multiplayer (both how to implement it and whether it should be implemented at all) and autopilot add-ons such as Mech Jeb (specifically whether they're helpful learning tools for new players, crutches that take away the fun of learning to pilot manually, or something that takes away the tedium of flying manually when you've done it so many times already; note that pointing out that it's closer to how real rockets are guided does not help).
A new classic is now "Hey, how about Lagrange points?" along with a proposal on how to implement them that's already been discussed and dismissed a hundred times.
Never bring up the topic of "female Kerbals" in any context whatsoever. Just don't.
Mentioning resources is also a great way to touch off epic forum conflicts.
Multiplayer is now officially in development.
As of v0.90, orientation autopilot (pro/retrograde, etc) and maneuver node hold are a part of vanilla game.
Memetic Badass: Nothing scares Jebediah Kerman, aka "the Thrillmaster!"
Memetic Mutation: MOAR BOOSTERS! has become famous in the geek community, referring to a common "solution" suggested by members of the KSP community when trying to increase the power of a rocket.
Weeks before a large update is released, fans frequently start a hype thread on the KSP forums in which they discuss the update. However, in 0.24 and on from there, there have been "Hype Vehicle" threads in which fans fight over/post image macros about "Hype Vehicles", vehicles that are powered bypure hype. The most argued about vehicles are the iconic HypeTrain and KSP's equivalent, the HypePlane. Here are the 0.24 and 0.25 hype vehicle threads, respectively.
Good Bad Bugs: The aerodynamics are a bit primitive at this stage, allowing for some wonky airplanes. For example, you can make one that is powered solely by flapping control surfaces. You can also make single-engine, air-breathing planes that can achieve orbit by fitting them with enough intakes. Said intakes do not even have to have a logical connection to the engine. They just have to be on the plane.
You can destroy planets with with struts! (Unfortunately fixed since that video's release.)
That One Level: While every planet and moon has its own unique challenges, a few of them have gained a certain amount of notoriety among the community:
Eve is probably the most infamous. It's deceptively easy to reach the planet, and its thick atmosphere allows you to land anything on it with parachutes using minimal effort. Returning from the surface, however, is a completely different story. High gravity and the same incredibly thick atmosphere which slowed your descent will also fight against your climbing rocket every step of the way for almost 100 kilometers, creating incredible amounts of drag and killing your engine's efficiency ratings. You can mitigate this a little by launching from a higher elevation, but designing a rocket capable of landing on and returning from Eve is still an incredible test of your engineering skills. Spaceplanes apparently have a slightly easier time of it, but those are a pretty good candidate for this trope all by themselves.
Tylo is a moon of Jool with a size and surface gravity roughly equivalent to that of Kerbin, but no atmosphere. Without an atmosphere to slow you down, you'll have to use your engines to completely kill your velocity in order to land safely, which will take a lot of fuel and effort. On the plus side, that same lack of atmosphere makes it relatively easier to reach a stable orbit... unless you burned too much fuel on the landing, which you almost certainly will the first time you try.
Moho is a large, airless rock in a noticeably eccentric orbit close to the local sun. All of this conspires to make it one of the more difficult planets to reach, land on, and return from. If you hit it at the lowest point in its orbit, you can easily zip right past it before you can lower your orbital speed enough to let it capture you.