'Sir' - it's a common misused word among male English teachers.

'Sir' can be used to address a male teacher or as a polite form to address a man but definitely NOT AS A TITLE (which people used to create themselves).

For e.g.,
Good morning, sir. (to address your teacher)
but
It's is wrong to say
You can call me Sir Hafidz. (as a title)
(*I myself misused it before because I was introduced by the principal to all the teachers and all the students by 'Sir Hafidz' and everybody seemed couldn't stop calling me with that title as they got so used to it.)

Instead, it should be
You can call me Mr Hafidz. 

Do you know why?

It's because 'Sir' carries a very big title that we do not have that qualification and not even eligible enough to carry that title like Sir Elton John.
(kindly check your dictionary for the definition of 'Sir')
So, you'd better think carefully if you intend to introduce yourselves as "Sir <your name>"

It's even a shame if your English is not even up to that level to be called by "Sir <your name>"