I struggle a bit with this issue, too. I grew up with parents who would ignore me a lot. I'd be trying to tell my mom something that happened at school, for example, and in the middle of it, she would turn to my dad and ask him a question totally unrelated to what I was talking about.
I sometimes wonder if that's partly why I became a college prof who liked to lecture about stuff that was not in the textbook. Then if the students weren't listening, they would get penalized by getting questions wrong on tests! Who knows...
I actually read that teenagers especially tend to get very upset if they text someone and don't get an immediate response. They tend to jump to conclusions like you folks were saying. I guess they have gotten used to an "instant" society. When I was growing up, all we had was a landline--and we had to share that with several other families. So, we might have to wait to even get a chance to talk on the phone or get a call back.
Have you ever had a pdoc or T who wasn't listening while you were talking? That really burns me. At least I can say, "Look I am paying for you to listen!"
As folks have basically concluded, often when we feel ignored it's not about us. Other people are busy with other stuff, wrapped up in things, etc. Case in point: My BFF told me she was going to her beach house and wouldn't have access to the Internet. We generally e-mail each other almost every day. I thought she was only going to be gone for a few days, so I got concerned when I didn't hear from her for awhile. Come to find out, she was gone for a whole week. At least I didn't immediately think I was no longer her BFF or that I had just upset her in some way, so I think I'm making progress!