A nod down with your head indicates respect and mutual deference. You do this with strangers to indicate your humility and non-agressiveness. With friends, you nod up to show your happiness at seeing and greeting them. They have brightened your day and you nod up to show that you are uplifted by seeing them.

Some guys seem to do it consciously as a way of communicating regard, diffusing tension, or simply saying hello without needing to stop and chat. Others may do it without even thinking about it, almost as a reflex.

Nodding can also be used as a form of nonverbal greeting or acknowledgement of another's presence; in this context, it is essentially an especially mild form of bowing, with just enough movement to show a degree of respect without additional formality.

In the simplest terms, an upward nod means a casual “hey” or “what's up”. Downward means “Hello, I see that you exist, but we aren't cool enough for anything more than that”. An unspoken rule about the nod is that it is rarely followed by any verbal exchange.

Nodding your head in greeting is a sign of respect, whereas lifting your chin is a sign of familiarity. Nodding the head is like deference to an equal or greater (alpha male). Lifting your chin exposes your neck (vulnerability) which shows you are comfortable with them when vulnerable.

When we greet others from a distance, we give them a slight head nod or we raise our eyebrows very briefly, the latter resulting in an expression known as the ‘eyebrow flash’.

In an ‘eyebrow flash’, the eyebrows rise rapidly for a split second and then drop again. The purpose of the ‘eyebrow flash’ is to draw attention to one’s face so that other facial expressions of communication can be exchanged.

The ‘eyebrow flash’ is used around the world as a long-distance greeting signal except in Japan where it is considered improper and impolite.

Culture can, and often does, modify the meaning our conscious body language gestures and facial expressions. Eyebrow flash is, without doubt, a conscious facial expression that we choose to give only to the people we know.

In linguistics, code-switching or language alternation occurs when a speaker alternates between two or more languages, or language varieties, in the context of a single conversation or situation.

Kill Haole Day is the term for alleged bullying incidents that occurred in most Hawaii schools, when non-white students would harass and attack white students. The incidents saw their height in the late 1970s.

I usually look most people in the eye and smile as I walk past them, usually get a smile back. Going to your question, it's perfectly normal to make eye contact, it's a natural thing to do, kind of like a quick glance before crossing the street.

So what do you do when you're actually walking toward someone? “It seems disingenuous to avoid any eye contact if you know someone,” said Riggio. “There are simple nonverbal cues that can indicate recognition, and that can include brief eye contact with a brief and slight smile and slight nod.

How do you do? Fine! A friendly greetin'.
How do you do? Say it when you're meetin'.
How do you do? With everyone repeatin':
Pretty good, sure as you're born.