That post really ought to be stickied.
No, you don't have to do anything. Frankly, it's troubling that you're building someone up in your head that you've never met solely based upon the fact that, at one point, one day, she wore a certain t-shirt. She's not avoiding you. I doubt she knows you exist. Maybe she does think you're creepy because you've just looked at her. (And, in all honesty? The line between creepy and shyly attractive depends an awful lot upon charisma and looks. I don't know where you fall, but you're doing yourself no favors by continuing to look without talking.)
Do what Llyranor said.
The librarian didn't reject you. You didn't ever ask her out. You asked, as far as I can recall, whether she had a moment to talk to you alone. Before that, you thought, for some stange reason(s), that she was completely into you. Both of these things -- the appearance of invitation and the illusion of rejection -- speak towards your difficulty with reading people. Midterms have nothing to do with it. You shouldn't even feel bad. Unless you directly ask someone out and they say no (or obviously demur), you don't really have the right to feel terrible about it.
No. You know what's creepy? Making a joke about being creepy!
Women are disgusting, flawed human creatures, just like men. Just talk to her if you want. But, as with the other person, it's one thing to irrationally fall hard for someone quickly; it's another thing entirely to fall for someone you've never even met or talked to before.
