According to Wikipedia, Sir is an honorific address used as a courtesy title to address a man without using his given or family name in many English speaking cultures. It is often used in formal correspondence (Dear Sir, Right Reverend Sir).
The term is often reserved for use only towards one of superior rank or status, such as an educator or commanding officer, an elder (especially by a minor), or as a form of address from a merchant to a customer.

So one should address a person with a Superior Position or Status, as compared to ourselves, as Sir.. And that is exactly what I used to do till December 2005..

Back then, I had founded a Financial Services company for providing Mortgage Loan products in Mumbai, in the month of November 2005.. My company was the Authorized Channel Partner of Citibank and it was the first Venture of my life..

Every month, as a practice, there used to be an Appraisal Meeting at Citibank (like any other Corporate) where all the Senior Managers & Regional Heads would gather to discuss Targets.. I was just one month old in the system and was meeting all of them for the first time to introduce myself..

It was the first Formal Business Meeting of my life and obviously I wanted it to be just Perfect, with the perfect First Impression and all.. So I had prepared a short paragraph on how I would introduce myself.. I was nervous like Hell..

When it was my turn to meet with the seniors, I was summoned to the meeting room where they had been sitting all afternoon.. Inside the meeting room, there was only one vacant chair and it was placed just next to the then Regional Director of Citibank..

As I sat besides him, he shook my hand and warmly greeted me saying "Vijay, right??".. And i smiled and replied "Yes SIR".. To this he said "Manoj".. For a second I couldn't understand what he said.. So I asked him again "What SIR??" To this he replied "Manoj, call me Manoj" (a little louder this time).. Honestly, at first I thought he was kidding.. So I politely replied back "Sir, how can I call you by your first name".. To this he said "This is Citibank, here everybody calls everybody by their first names"..

He further explained me that in an Organization nobody is Superior or Inferior depending upon their Position or Seniority.. The Organization functions properly when Everybody does their respective Jobs well.. And everybody holds the Position that is best suited as per their Capabilities & Profile.. So even if I am the Director and probably take some of the Key decisions in the Organization, I am not doing something extraordinary.. That's my Job and I get duly paid for it.. And hence, you are not liable to call me SIR.. Now go ahead and introduce yourself..

Well, after that Inspiring Speech, I had almost gone blank.. But somehow managed to introduce myself..

Since that day I have made it a point to address everybody in my Work Circle with their First Names.. Some people, who are Superior to me in Age and/or Profession, feel awkward and offended.. But some of them really understand my true intention of communicating an Equality in the Work Environment..

After all, we don't have the concept of a Superior Entrepreneur or an Inferior Entrepreneur.. We are simply ENTREPRENEURS.. :)