One of my favorite passtimes is to start with a premise, and work out a theory that, to all MY knowledge seems proper and correct.
Creepiness comes in 2 flavors. One is either creepy or a creeper. Being creepy is something you do. A creeper is something you are.
Let me expand.
Let's say you're sitting on a subway, hurtling through the bowels of some big city. (I've never been on a Subway, aside from eating their sandwiches and riding buses. That along with reading about subways makes me pretty near an expert, don't you agree? That's what I thought...)
You're standing by one of those post thingies, holding on for dear life because there aren't any seats available. All of the sudden, a hand that can only belong to the man behind you cops a feel through your gray tailored suit.
Ooowee!! That was creepy! We can therefore say that, in preforming a creepy act, that our man is creepy.
A creeper is different.
Same scenario: You're on the subway, seated this time, and you get a funny feeling. You look over to your left and see a man in a black coat and black felt hat. There's something off about him, but you can't quite put your finger on it.
Maybe later you find out that he is a peeping tom, or that he steals and strokes ladies'....underthings....
But that is not why he's a creeper. Being a creeper is full time. A creeper is necessarily one who performs creepy acts. They can't help it. And it's not the act that tipped you off. You knew instinctively. (If your creep-o-meter isn't malfunctioning...check those batteries folks!)
More extremely rational theories later...