Ah, slender man... I don't get creeped out easy but paradoxically manage to creep myself out constantly. Slender man is one of those things that did initially creep me out, then I got over it, and then it started fuelling my self-horrifying side. For example... I have a small gap in my curtain, but I never bothered fixing it because it only looks on to a very, very small portion of my room. Unfortunately that portion of my room includes the back of my head at this moment. And as soon as someone mentioned slender man, I immediately felt like he was watching me through it.
But don't worry, I looked. There's noone there. You might want to check your windows though.