"Fuck whatever you are doing, I want to talk to you right now for not reason at all" is not a very polite message to pass.
If people make themselves uncomfortable just so they can clearly tell you that they do not want to talk to you... it may be because they don't want to talk to you.
Someone with headphones on does not necessarily mean they wouldn't want to chat. And a wave doesn't necessarily mean the waver wants to chat either (I don't mean waving right next to someone to get their attention)
It's like fishing. I don't HAVE to do it. But I enjoy the atmosphere. It's one of the last things I have left in this world from my youth. I spent almost every free minute I could in school in either the library or computer lab.
I have absolutely no idea at all. Completely blank. I'm not American, so it's most likely a difference in culture. Chatting to people I know, has always been a pleasant experience.
/I'm serious, I'm completely oblivious to how it's assholish behaviour to talk to people I know-