What's the deal?

I was so angry earlier today while I was out running some errands. I was buying a birthday card for a friend at a local CVS. First of all, I hate going into this particular CVS...actually I really don't like going into any CVS. Every CVS that I have been in is always so congested and crammed with so much crap that you can't just get in and out. Anyway, surprisingly enough, I found a nice card pretty quickly and went to pay for it at the registers. I usually try to use the automated, self-checkout registers because people usually don't use them and I can make a quick getaway without dealing with the wonderful and helpful clerks (which is a whole different rant for another time), however, today they were both closed. So I got in line behind another customer and waited my turn to pay. As I was waiting, a woman moves in front and next to me off to the left. Now I'm usually pretty courteous and I assumed that she was just going to ask one of the clerks a question...but oh no! This woman got right in front of me and paid for her items...she didn't say anything to me! At that point I was fuming! So I moved over to another line and waited my turn again. As I was waiting, she turns and starts toward me and looks me straight in the eye and says NOTHING! So I say to her..."thanks for getting in front of me in line!" And she just stares at me...she doesn't even say "I'm sorry," "excuse me," or "oh, I didn't see you there," absolutely nothing! What's wrong with people? Now I know that this is not an "Earth shattering" ordeal, but why are some people so inconsiderate and basically stupid? It makes me so mad! Sorry, I just had to vent about this story...because it happens all of the time and I'm so sick of it. Thanks for listening to my rant today...I feel a little better.