@AlexF That's definitely not a worldbuilding question. If I understand you correctly you're asking how to write dialogue where a character asks to be referred as "Mr. [lastname]. You may want to look at Writing and Interpersonal Skills but I don't think the question as written would be a good fit for either of those sites either. Makr sure you read their help centers before posting.

@sphennings Thanks for the input. I'm getting the sense to just avoid SE with this one