You will need
  • - compliance with standards of business ethics and generally accepted norms of politeness.
The first thing is to understand well any Manager: the rule "I the chief - you the fool - viciously. Every demand, claim, etc. must be substantiated.

In this "part of your duties" or "does not meet corporate requirements" is sufficient argument, but that really is not consistent.

If the employee proved that you are wrong, admit it not ashamed. Shameful to appeal to the chain of command, knowing they were wrong.
The fundamental question for many is how to address each other: "you" or "you". Here you need to understand that the tradition appeals to a subordinate to "you" and by name while demand response "you" and first name and patronymic inherited from the party-Soviet apparatus (and current officials so accepted), but the best of it is not true.

If the company made an appeal to "you", because subordinates should speak, the transition to "you" is only valid mutual. So taken, in particular, on the Russian subsidiaries of Western companies to the authorities call "you", and his patronymic I do not know as superfluous. Unless this is not comfortable to the employee.
A subordinate is unacceptable to raise your voice. The same goes for insults.

Even a relatively innocuous comparison in the spirit of "the quality of the trainee" should be avoided.

If work must be redone, the employee himself will draw the appropriate conclusions, it is enough to point out to him what is objectively wrong.