In the Wizard of Oz, munchkins are a race of bizarre diminutive people who behave in ridiculous ways. In role-playing gaming, a munchkin is a player who plays in a selfish or aggressively competitive manner, trying to gain the most power, loot, or points. Such a player is considered to be acting childishly, they are not playing in the spirit of the game. More recently, the term has lost some of its pejorative meaning. There’s even a Steve Jackson Card Game of this name (see illustration).
There’s a third, less well-known meaning of munchkin, which is a competitive scifi fan or nerd who is only interested in the most powerful spaceships, or super-soldiers, or weapons. I can’t say this is an official term in any way. I first heard it in discussions in the Orion’s Arm Worldbuilding Group that I founded with some friends back in 2000; I can’t recall who coined it in this context.
Obviously, any advanced civilisation is going to have super-advanced technology, and hence a lot of power. But worldbuilding and storytelling isn’t about who has the most powerful ships or the biggest guns. It’s about creating a believable setting, with believable characters.
Munchkinism (as here defined) is also tied in with “versus” arguments. These originally (about 18 or 20 years ago) seemed to take the form of often heated arguments by fans of different franchises about whose franchise is better, most often Star Wars and Star Trek, a bit like “my dad can beat up your dad”. The tendency now, on YouTube and elsewhere, is towards more good-natured discussions, e.g. who would win between Superman and the Incredible Hulk.
A quick rule of thumb is, the lower a setting is on the Mohs Scale of Science Fiction Hardness (i.e. the more ridiculous a universe), the more power its strongest superheros, ships, empires etc have. So Bugs Bunny is more powerful than Superman (for example Bugs can step outside a cartoon and draw a kryptonite anvil around Supes’ neck), Superman is more powerful than the Star Wars Empire, Star Wars capital ships are more powerful than those in Babylon 5, and so on. Or in other words, the greater the power level, the greater the sillytech.
Even though I prefer more realism (a higher Mohs Hardness) in science fiction, the appeal of munchkinism in at least moderate proportions cannot be denied. Small spaceships may indeed be far more realistic than giant ships, but giant ships are more awe-inspiring. Using Mechs rather than tanks would be ridiculously impractical, as they would be highly vulnerable on the battlefield, but the trope still has universal appeal.