Mr. *Insert First Name Here*

[Tuuvi]

Trying to show respect?
Addressing someone you're not all that familiar with by using just their first name can be viewed as a sign of disrespect. When I briefly worked as a teacher I addressed all my colleagues as sir/ma'am, and they all addressed me as sir irrespective of their age.

Edit:
Though I do remember reading a Nevil Shute novel as a kid where a Brit visiting the USA is requested to stop using mister after the first time he addresses someone. But I'm pretty sure the members from this side of the pond would agree with me.

Here in the States "Mr." isn't usually used between coworkers, friends, and significant others, and when it is used it's used with the last name and not the first.

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Vuk it sounds to me like "Mr Vuk." has become your nickname, I wouldn't get too upset over it.