Did you note, how important looks are, while creating the first impression? A person does not know anything about you and does not have any idea on your qualities before meeting you. The first thing that he notices about you is the way you look.
Organizational Behavior can vary greatly from company to company but it comes as a surprise to many people that organizational behavior can, and does vary, appreciably within a company too. Etiquettes will also vary from person to person depending on whom you are interacting with.
For example, the body language, correctness of speech, right selection of words, and clarity in presentation will vary when you talk to your boss, or your supervisor as compared to a colleague who is of the same level as you.
You will feel even more relaxed when the person is a close friend. Similarly, you could easily skip a few steps in decorum when your friend invites you to your place. If your boss invites you for dinner, your etiquettes will be different.