My feelings hearing \"Hi\" to someone

When I met someone at the first time and he/she says \"Hi\", I feel very awkward. Because I\'m introvert person and I don\'t have any information about him/her, so this situation makes me uncomfortable. But there are some cases I can adjust this situation. First, I don\'t care that my friend\'s parents say \"Hi\" even though we meet first time. Because I\'m younger than them, and I get informations who they are to my friends. Second, I don\'t care that strangers says \"Hi\" in my office. Because I\'m a junior, and there are so many senior members in my office. So It\'s okay that senior met first time says \"Hi\" to me!