Use a Tissue! Please?

Here's a question: What is with our ability to isolate ourselves from the world? This sounds far deeper than what I'm really asking, so I'll try again. How do we get so stuck on ourselves, that we forget that other people can see/ hear us? You see it in cars, in the cubicle at work, in the coffee shop, in the library, etc. We seem to be so lulled into complacency by silence that we forget that we aren't invisible, even if we feel that way. I am talking about picking your nose, randomly bursting into song (I'm guilty of this one. No, we are not on Glee...) scratching yourself in places you should wait on, and picking your nose! (That one is so gross, I feel the need to mention it twice.) This is not an exhaustive list by any means, but these are the ones I've seen recently. Forget professionalism here for a moment. Is is really so easy to be so ignorant of your surroundings that you do anything that you feel the need to, at the moment the whim hits you? I hope I never lose my self-awareness to the point that I start picking my nose sans tissue and manners in a public place.