The Fairbairn-Sykes fighting knife (which is perhaps one of the most iconic knives ever made) comes with a sheath which fits the knife like a toothpick fits inside a size 20 sock.....It literally rattles around like a thought inside a supermodel's head.
Then again so many of these come from Sheffield blunter than a butterknife so it's swings and roundabouts
Also the Cold Steel Kobun comes with a kydex sheath designed (it seems) specifically to blunt the knife every 4 times you draw it.
It literally needs another 5mm clearance on the edge side of the sheath to go from "ARGH!" to "Awesome"
That said- Cold Steel's Chaos series have an excellent iteration of the kydex sheath theme- but deary me- that knife is heavy, poor balanced and terrible at cutting. It's like I'd say it'd be good at knocking nails in but they put an *ahem* 'skull crusher' pommel on it so it won't even do that well.
Though it will make a reasonable paperweight.
Warhammer 40000 is- basically- Lord Of The Rings on a cocktail of every drug known to man and genuine lunar dust, stuck in a blender with Alien, Mechwarrior, Dune, Starship Troopers, Fahrenheit 451 and Star Wars, bathed in blood, turned up to eleventy billion, set on fire, and catapulted off into space screaming "WAAAGH!" and waving a chainsaw sword- without the happy ending.