OP would have to be pretty oblivious to life if he needed feedback for that interaction. He saw that someone was in a conversation, tried to interrupt, and then was offended when that someone didn't want to be interrupted. Look, if someone's doing their own personal business, don't try to interrupt. And if you do, at least be understanding that they had no obligation to stop what they were doing just to humor a stranger, so there's no right to be offended.