Do you know who you're talking to?

Man joined a big Multi National Company as a trainee.
On his first day, he dialed the pantry and shouted into the phone :
“Get me a cup of coffee, quickly!”
The voice from the other side responded:
“You fool, you’ve dialed the wrong extension!
Do you know who you’re talking to ?”
“No” replied the trainee.
“It’s the Managing Director of the company, idiot!”
The trainee shouted back:
“And do you know
who YOU are talking to, you IDIOT ?”
replied the Managing Director indignantly.
replied the trainee and put down the phone.