For a time I lived with a "witch". Not entirely sure if she even had much definition to what kind she believed, or what she drew from, but she made much out of it, even accusing me of persecution. (I simply disagreed, but let it go). Anyhow, as she was moving out, she hung a scissors by a string, pointing down, above the front door, on the inside of the house.
It was hung from a bulletin board tack, which I thought was unsafe, so I took it down. A day later, she put it back up. I took it down again. I found out that it was related to her beliefs, because she left me a nasty note about interfering with her right to practice her religion. I told her that I didn't like the idea of a poorly hung scissors clipping someone in the head, and after I found the scissors up again, I took it down. But this time, I replaced it with a banana. The next day, she had replaced the banana with a Santa Claus christmas ornament, which made me laugh, so I guess good humor won the day.
Anyhow, It's left me honestly curious about it. Do you have any idea what "scissors over the door" means? I'm not aware of anything regarding scissors, although a google search brought up a few links about old superstitions about hanging scissors over a door. It was meant to keep evil influences out of the home. Why your roommate would do this as she was moving out is beyond me, but it sounds like she was crying for attention with all of her leaps of accusations of persecution.Ironically, the scissors as ward-against-evil had strong Christian connotations. The scissors were hung by one loop so they would hang in the open position, like a cross. Also, some websites state that the gesture was supposed to keep "witchcraft" out as well as evil influences!
http://www.catalogs.com/info/gadgets/the-history-of-scissors.html
I think replacing it with a banana was pretty awesome, actually.
It's an example of the use of iron, especially but not always sharp, to ward fairies, demons or whatever other bad spirits exists in a particular belief system (so of course, to someone who believed witches were supernatural evil-doers this would include witches, otherwise it would not). The horseshoe above the door, the billhook at the window and the scythe in the thatch are better known examples.
It was once common to hang open scissors above a crib for the same reason. Frazer's examples of iron are worth reading here (for all of Frazer's many faults, in this case a mismash of randomly compiled disconnected examples serves the question well enough).
TBH, the problem seems to me not to be that someone was hanging up scissors, but that they were hanging them up badly. I'm all for using sharp metal things for protection, but just like when you do so in the mundane uses of sharp metal things, if you aren't careful they cause more harm than they prevent.