39. Bowel Movements: That pushing and wriggling in your belly doesn't mean you're pregnant. It's your guts, tired of their boring parasitic relationship with you. They want out, and they get out in the most disgusting scene ever put to film. It makes the goatse man mild in comparison. The pulsating worm-like creatures make it on their own by, ironically, eating people.
40. Weredog: A young athlete devotes his life to training, but can't seem to win anything. Broke and with a failing marriage, all he wants is to come out on top, just once. After getting slobbered on by a strange looking stray dog, he finds himself with unusual hair growth and a hankering for Snausages. He begins to get shorter, a fleshy tube grows out above his ass, and he finds himself screaming uncontrollably whenever an ambulance drives by. One morning, his wife wakes up and finds herself cuddling a shih tzu. She enters him in obedience and agility competitions, working up through the ranks until the heart warming finale when her husband finally wins the national championship.
41. Binder Rings Snapping Shut on Your Schlong: You know how 3-ring binders have those clips that are very sharp and snap shut very fast? That would really hurt if they snapped on your dick. Maybe a psycho could use one as a weapon, chasing people with a binder and being all like "I'm gonna snap this on your penis".
Oh shit...am I running out of ideas?
See also: 100 Original Ideas for Horror Movies, #30 - 34.