Dogs - When not rabid, dogs are heroic creatures that will die trying to save you towards the end of the film.
Drugs - If you do drugs then you will die. Not because of the damage they do to your internal organs but because of the fact that a homicidal maniac can smell a junkie a mile off. (See Taryn White in Nightmare on Elm Street 3). The smell of marijuana is like catnip to a killer.
Dragons - Dragons are huge beasts that all talk like Shawn Connery. They exist in deep underground caves in Wales and, if you unleash them upon the earth, you will have to get a young Christian Bale to save you.
Dagon - An evil demi-god that smells of fish. If you live near the sea then there is always a chance that you will encounter Dagon, or one of his minions. In such situations, you should reduce him to tears by explaining the current over-fishing crisis that affects many regions of the world. Together you can then join Greenpeace and fight for a better world (Or have golf balls hit at you by an angry Bruce Willis on an oil rig).
Denmark - A great place for bacon.
Darth Vader - Should you find Darth Vader wandering around in a horror movie, please direct him to the Science Fiction department. With his large mask and helmet, he has a tendency to get lost. Please ensure that he also takes his asthma medication.
Danny DeVito - This diminutive actor is not all that he seems. In fact he is a secret embassador from the planet Zog. His regular reports on humanity and its exploits will later determine our fates in the wider universe.
Demons - Ugly creatures that like to insert themselves inside little girls...Gary Glitter is a demon and can be identified by his pointed beard and prepensity for glittery pants. Demons are also big fans of obscenity and green vomit. It was once thought that George W. Bush jr was a demon, hellbent on destroying the earth, but it was later determined that he lacked appropriate intelligence.
Derp - See George W. Bush jr.
Derpette - See Sarah Palin
Danger Signs - In horror movies, it is a requirement that all danger signs be erected amongst large, overgrown foliage where they cannot be easily seen. Alternatively they can be written in a foreign language.
Dinosaur - If an island is deserted for long enough, it will attract Mad Scientists that wish to populate it with prehistoric creatures. These creatures will eat you, even if you manage to hide in a poorly-built toilet cubicle. You can spot the prescence of Dinosaurs by huge mounds of poo or by anyone that claims to be a paleontologist.
Dracula - Like all foreigners, Dracula likes to take our women. Whether he will later move on to take our jobs is unknown. If you encounter a man with a slick-backed hairdo from the 20s, then you my be in danger of a vampire attack. If said man lives in a large Romanian Castle then you can be sure of it. One has to wonder if the undead have to pay property taxes.
Dinner - Never agree to eat dinner at the home of strangers, especially if they live in the middle of nowhere. There is every chance that you will be eating the remains of your friend that mysteriously went missing earlier on.
Dead Body - Never lean close to a dead body. If it is a zombie, it will bite you. If it's not then it will just smell really bad.
Diamond Mines - If Tim Curry approaches you to help him find the lost city of Zinj then you should walk away slowly before turning to run whilst shouting 'Congo sucked, you were better in IT.
Deserts - Deserts are not happy places. They are home to inbred pychopaths, Nuclear testing sites, and many episodes of The X Files. Plus getting sand in your underwear sucks more than anything. After an hour alone in the desert you will be praying for something to come and stab you to death.
Daniel Larusso - There are many situations in which the Karate Kid would be useful, but in a horror film scenario, a flimsy Crane Kick just isn't gonna cut it! Mr Miyagi on the other hand...
Devil - The Devil is in the details, so avoid instruction manuals at all costs.
Deadites - Freaky-ass zombie/demon hybrids that live in the woods. You can either hire out Bruce Campbell for the day to deal with them, or alternatively attach a chainsaw to your left hand whilst holding a book of witty one-liners in your other.