Who here has tried the famous:Say bloody mary in the mirror three times then she comes and kills you! Who here has been gullible enough to try it. I have!
I have to say, the whole thing is ridiculous. Unless someone can prove that such an incantation would summon a murderer, I have no reason to be afraid. However, I still wouldn't do it, because someone would probably jump out and scare the living crap out of me.
I tried it before, but I never saw anything. I would laugh if I actually saw her though (not really, I would be screaming and wetting my pants like "...AAAAAAHHHHHH!!! XP"
I tried it once when I was young, all you see is a remnant of light in the back of your eye. I suppose if I was really expecting to see a ghost woman in the mirror my brain might interpret that light as such.