This definition is only directed towards young men, it is not meant to be offensive to girls: "creeper" is a term typically used by young women, usually young women who like to party, which means "I am afraid of you because you are by yourself", or, "I am afraid of you because you are not socializing." I've noticed that women tend to label men creepers if they have dark features, such as thick eyebrows or a distinctively superior look. Something else I've noticed is that older, more mature, and usually brunette women are actually ATTRACTED to these types of men. Think about it, young men who have dark features, are independent, and mysterious, seriously, I guarantee you will win the love of a beautiful women, and dont even worry about being labeled a creeper, you will learn later that it's a compliment.
Being a creeper may be when you're at a party where you feel like you don't fit in with the girls there, and not wanting to talk to them so you just chill by yourself or with your guy friends.