Am I bad at proper social etiquette?

[Anna F]

In my college class, I am very quiet and I keep to myself a lot. There's this girl who is really nice and actually makes an effort to be nice and strike up a conversation with me. I was up late doing a paper and I was in a zombie-like state all day. As I was leaving class to go home, she holds the door open for me. I say "Thanks." She says "Hey" and I say "Hey" back. I take a step to go on my way and she pulls out her earphones and says "What are you talking about?" I got confused and thought that she didn't hear me say "hey" or she thought I said something else. I turn around and see there's a girl walking by and I assume she was talking to the girl, not me, and I walked away. As I pondered the situation I realized that I had, unknowingly snubbed her. She was talking to me. She was actually asking me what I was going to talk about in my speech. I couldn't go back and talk to her because I'd gone the other direction. I feel really bad. I don't talk to her in class.
I have class with her again this Thursday but we'll all be doing speeches and not able to socialize. I feel like I should apologize to her or explain myself. But I am afraid that she would think it was weird if I walked up to her without ever talking to her before and explaining that odd situation. She might just ignore me or forget the situation but I am deeply embarrassed and upset that I snubbed such a nice person.
How do I go about trying to explain what happened to her? Should I just forget it?

[rememberthesalamander]

Haha don't worry things like that happen to me all the time at my college. You're not a social misfit, just a little shy. I remember once I was eating at one of the lunch halls with my roommate my freshman year when he told me that a girl had said my name and waved at me and that I had turned my head kinda in her direction but didn't say anything. I was zoning out at the time and didn't even realize someone had called out to me. It was the meanest thing I've ever done and it was an accident. I think I know who it was though because even now 2 years later a girl who I used to flirt with won't even look at me. I'm not sure it's her though because I do stuff like that all the time. My advice is too just confess what happened, because I wish I had done that at the second my roommate said that to me.

[Robyn Dana]

write a quick note.
not a long gushy one like to a best friend just "hey sorry about the time.... i was so tired and stressed. i wanted to a apoligize... blah"

[I Love Howie Carr]

Just say hi to her again, if you really want, but you were not rude. It's actually rude of her to be listening to music so loud she can't hear people. It's also dangerous. If a fight was breaking out, shots were fired, the fire alarm rang, a car was skidding up behind her.....whatever, you can imagine all the scenarios where it would be smart to hear what's going on around you.

She's obviously not interested in being polite or safe and apparently wants to be left alone so badly she's willing to sacrafice her safety & manners to do it....so don't sweat it, but again, if you really want to talk to this silly person, just say hi when you see her & see what happens.