“Tu ” and “vous ” are two ways to address someone as degrees of intimacy, familiarity , friendliness .. The passage of the informal “you” to the polite “you”, and vice versa, creates an impact on relations.
In general, use the polite “vous” when you meet for the first time. The teenagers use the informal “you” for talk each other. Between boys and girls for example, there is not discomfort in this respect.
The “you” in work, is not the same tone as the familiar «you” in a personal relationship, which implies intimacy, companionship, closeness and equality. “You” professional, like the “you” English is a kind of neutral, practical and functional.
In a first meeting, the choice between you formal and unformal is not always easy, there are circumstances where it hesitates, and where a solution must be found verbally. There are some cases where a person is authorized to use the informal “you”, while its partner, gives an answer with the polite “you”. These situations do not allow the person to use the familiar “you” with his interlocutor in turn, showing that the formal mode is not only a mark of formality, but also an indicator of social hierarchy that show the respect.
Even if the first contact is warm, it is safer to use the formal use, until you find a protocol. In general, it is the oldest person, or one that is in a supervisor position, or the person who receives that will decide: “We could perhaps talk to each other in a more familiar way?? “…