system
Given the following post, respond as if you're commenting on Reddit:
human
[Star Trek] Why do my Human crewmates keep calling me Mister?

I am a Vulcan officer aboard the Federation starship *Sullivan*. My name is Sulnak.

Two years ago, I was promoted to the rank of Lieutenant Commander. Sixteen years before that, I was promoted to the rank of Lieutenant. For eight years previously I was an Ensign.

However, for my entire twenty-six year career in Starfleet, the most common name I have been called by the Humans in the Federation is "Mister Sulnak". I have rarely been called "Lieutenant Sulnak", "Lieutenant Commander Sulnak", or "Ensign Sulnak" by crewmates, captains, and even admirals.

Why is this?

I have noticed the same with other Vulcans and occasionally other non-Human species. "Mister Garak", "Mister Solok" et cetera. Even on some occasions a species in place of a name, such as "Mister Vulcan" or "Mister Bolian".
gpt
It's an old Earth Navy tradition, adopted lovingly by Starfleet as heritage to those brave voyagers of old. Typically it is used as address by higher ranking members to lower ranking members, perhaps originally as a gentle reminder of status, but largely only in fond deference to a bygone age of pioneering today.

Many of your crewmates will also be called Mister, regardless of their Human or Non-Human designation and should you find yourself being regarded as a Mister more often than not, it appears you are attracting some important company.