Pinhead - After a particularly bad injury at work, Pinhead sued his employer and used the procedes to set up a batchelor pad in Hell. His Thursday night parties are becoming increasingly popular and Johnny Depp is known to be a frequent attendee.
Pumpkin Head - Again, after a particularly nasty accident at work, Pumpkin Head sued the farm that he worked on and used the procedes to set up an entertainment company. He is available for weddings.
Pox - If someone in a horror movie comes down with the good ol' 'pox' then it would probably be best to call a Doctor or House MD. Despite Hugh Laurie's utter rudeness, he will find time in the last five minutes to have a wonderful breakthrough and cure your condition.
Prostitute - Prostitute's typically get murdered in horror films so if you ae a hooker, I suggest that you stop. Giving massages with 'happy endings' may be okay but make sure that the only reason you are doing it is to pay your colleg tuition - this is the only acceptable reason in a horror movie if you wish to live.
Pistol - If you are based in the 1940s up against demon-possessed Nazis in an ancient castle then a pistol may be a common means of defense. In a modern-day horror film however they are a little bit girly. You should replace the pistol with a 'hand cannon'.
Pasta - Pasta is a healthy, easily preserved staple food that is ideal during a zombie-siege situation. Macaronis is best but fusilli will suffice in a pinch. Zombie surivors cannot afford to be picky.
Police - In a horror film where you are being held captive, a police officer will always come to question your tormentors but will then leave, satisfied with the answers. Just as the officed is about to get in his car, you will manage to knock something over in the basement and alert him. By this time, however, it is too late and the officer will then turn around only to be stabbed or shot. Makes you wonder why they always decide to investigate kidnapping cases solo.
Parasite - Someone that collects wellfare could be considered this, but in a horror movie they are typically little slug like creatires that enjoy entereing people's noses or eyes. The best bet is to burn them, or get really drunk to dehydrate them if they are inside your body. Lady Gaga is infected with several martian parasites and this at least explains her fashion choices.
Paris Hilton - Paris Hilton is a biological weapon constructed by a terrorist organisation to infect all human males with syphilis. Her mission is simple: sleep with the entire male population and destroy us all.
Pigs - Pigs are cute, but pig-masks are not. Someone wearing a pig-mask will undoubtedly wish to kill you so run away. Rosie O'Donnel is not wearing a pig-mask - that's just her face.
Puppies - Puppies are the cutest thing know to man, but in a horror movie they will always end up dead, hanging in your closet. As a result, all puppies are henceforth banned from horror movies.