Ohhh it all depends on her tone. If she seems like she's creeped out, she's telling you she thinks there's something wrong with you. If it's all in good humor and you're 100% sure she sees it that way she's kidding around with you and she doesn't have a good come back to what you just said so she uses the cop-out answer :P I do it all the time when I mean it the second way. "You're such a weirdo" or something like that. It can be affectionate, depending on tone.
Biggest insult she can give you. It's the equivalent of loser, creep, ugly, or I have no interest in you. Frankly, I'd rather be called a jerkoff or douchebag than "weird." Treat a girl like sh*t and she'll stick to you like it ;)