y do v greet someone on meeting them ... for eg hi ? hello??

it's a civilized way to start a conversation

Greetings are social customs or rituals to show attention or to confirm friendship or social status between individuals or groups of people meeting each other. Greeting habits are highly culture- and situation-specific and may change within a culture depending on social status. This topic excludes military and ceremonial salutes but includes rituals other than gestures.

Some epochs and cultures had very elaborate greeting rituals, e.g., greeting of a king.

Secret societies have clandestine greeting rituals that allow members to recognize common membership.

http://en.wikipedia.org/wiki/Greetings

Try going a day without greetings and then you tell us.

i only greet the people i know.

it is the social etiquette and comman manners that makes us do it.

what would you have us do, just stare at them & hope they read our minds. yiiiiii.