Why do girls think I'm creepy & weird?

I'm an 18 year old guy and really frustrated. Girls seems to think I'm creepy & weird. I can go up to pretty much anyone and talk & be comfortable like I've known them for a while, maybe that's what's weird. Like go up to a girl I don't know and say "Hey what's up?" with a smile and then chat. I try to always be nice and respectful. Not a pushover, but kind and considering of their feelings. I'm not one to go up and randomly flirt with girls at school, THAT would be creepy IMO.

But often times, I find out a girl finds me creepy, usually after talking to them. Like yesterday, I was hanging around and talking with a group of girls. Just chatting, and I thought having a good time. Well, we were talking about Twitter, and I was like "hey, what's your Twitter name, I'll add you?" She gave me her twitter name and I did add her. Anyway, later I saw on my Twitter feed her and her friends were talking about me. She was talking about how she was trying to block me and they were joking that "I hope he doesn't show up at our house lol". I find that kind of hurtful. I'm not even sure what I did wrong, aside from hanging around them and chatting.

Not all girls think I'm creepy. A few like me and think I'm nice & funny, but I'm just not interested, I'm not attracted to them. I don't think my standards are too high. I mean, it's 11:30 and I've already talked to 4 girls I'd like to date. They're all relatively attractive, not necessarily model type, but they're "cute".

I'm just curious over why girls think I'm creepy and weird? Maybe it's my personality. I tend to come across as timid to people I don't know well, only because I'm kinda shy. I open up once I get to know people though, However, I make an effort to be outgoing, so maybe outgoing + shy comes across as creepy? Idk, I'm just guessing here.
Why do girls think I'm creepy & weird?
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