Suspension of disbelief

If anyone's even out there... what typical elements of your game of choice do you have a hard time buying into? Me, I'm a D&D girl, but... I just cannot into dungeons above a small "lair" size and population, unless they're so big as to be an environment unto themselves (like the Underdark). Those of us that have crossed paths with Mike Mornard have all heard the story of how he deflected the question of what the monsters in his dungeon eat by putting a McDonald's on the sixth level of it, but (as non-seriously as I normally take my gaming), even then I tend to fixate on how a handful of goblins are going to navigate through all the intervening hazards that presumably exist between his lair on the first level and Mickey D's on a regular basis. Feel free to describe setting elements (from any game) that stick in your craw, or try to disabuse me of my notions, or whatever.