This guy freaks me out ONLY because he always reminds me of a recurring nightmare/sleep paralysis vision/hallucination I had as a kid. For years I repeatedly found myself briefly seeing a figure that I grew to dub "the Tall Man".
Basically Tall Man was a basically humanoid figure, but unnaturally tall, taller than any man I'd ever seen, and insanely thin to the point of impossibility. I used to reguarly witness him in my dreams, even normal dreams, just in the background. Even IF I forgot the dream, I always remembered if He was in it.
Like once, all I remember of one dream was a chain-link fence in the background, with the Tall Man standing behind it in shadow (he was always in shadow) looking at me.
Sorry, this has turned into me ranting about my childhood nightmare figure.
Basically, Slender Man freaks me out.