Colloquialism and communication

What do you say (and how do you say it) when you meet
someone for the firstime in a day?
a) Hello.... how are you doinggg.......?
b) Hey dude.... how u doinn!!

What do you say (and how do you say it) when asking for beer?
a) Excuse me... can you please hand me a can-of-beer?
b) Hey brother... cud u grab a beer for me...?

The answer, in each of the cases, is "it depends".

Choice "a" is more formal and suits when you are engaged in a formal conversation. This language is appropriate for discussions in business meetings, when greeting someone for the first time, or when showing respect to the listener.

Choice "b" is colloquial and showcases your friendly nature (or informality). This language is best when talking to close friends, when in a party, or when being friendly to the listener.

Even though no strict rules apply when to use one choice over the other, one should pay attention to the type of audience when choosing between "a" and "b".