At work and with family: full first name
With wife: shortened first name
With friends: last name (there are several in the group with the same first name, so we go by last name)
My last name is Beitz (pronounced “bites”). I used to go just by that until I started working with a guy who’s last name was Geitz (pronounced the same as mine only with a “G”). On several instances things got mixed up.
My first name is hyphenated Peter-Paul but I never use that as it’s quite stupid having a hyphenated first name and plus if I used the initials people would call me PP Bites. And that doesn’t sound too good. Not that Peter Bites sounds any better. Also, my brothers name is Paul and on rare occasion things got mixed up when someone was looking for one of us.
My middle name is King. But using that sounds either narcissistic or like I’m the family dog. And going by King Bites sounds cartoonish.
So I just go by PK.
I answer to Kathleen, Kathy, or Kat. Which one I’m called tells me where and when in my life I know you from. My mom tried to call me Kate when I was little but I wouldn’t answer to it.
Most people use the common shortened form of my first name. Two of my aunts use the common “child” version of my first name. An ex-girlfriend from college used my full first name, which should have probably been a sign that relationship was doomed.
My students used to use Mr. ______. At my current school it’s common for teachers to go by first names, and that lasted for a time, but now many people at the school uses my initials.
I don’t have a nickname and don’t want one.
My middle name is merely pro forma; I never actually use it except on forms where they insist on it.
I’ve endured a lifetime of Americans bungling the pronunciation of my Sicilian last name, even though there’s nothing difficult for English speakers in pronouncing it. It’s just that when people see an unfamiliar non-Anglo name, they get their brains short-circuited and start stuttering. I do think people in general are pronouncing it better in recent years. When I was young America was less ethnically diverse and more whitebread, but we’ve had decades to adjust to non-Anglo names and by now people in general are actually better at getting it right. But my first name is just a regular, familiar first name in English and it amuses me if anyone hypercorrects and tries to pronounce it like a foreign name. That’s trying too hard.
I like my first name a lot and use it everywhere, always (except online).
First name 99% of the time (Julia).
Close friends call me Jools, which isn’t really a nickname, just a derivative of my given name.
I always use my first name. Many people turn it into a nickname without asking me. I quit trying to correct them a long time ago. (My father has the same name and goes by the nickname exclusively, so my instinctive reaction when I see my name shortened is that it’s him and not me.)
People call me by my middle name, or by a shortened version of it, and always have. If it weren’t for all the post-9/11 crap, I’d never have to use my first name at all, but now the government, and anything remotely security-related (e.g. airlines) requires firstname middlename lastname, so I get called by my first name a lot more nowadays than I used to be - pre-9/11, I could leave my first name out of practically anything other than direct interaction with a governmental entity.
But I’m still middlename lastname in enough places that it can sometimes be a problem - “it says there you’re firstname lastname, but it says here you’re middlename lastname, our computer can’t deal with that, and just who are you anyway” - that one of these days, I may just have to drop my first name. I share that name with my dad, though, so I would probably wait until after he passes away.
Sometimes I find it interesting how little I have to say my name to anyone. You can get by in most situations without exchanging names verbally at all. And official situations they likely have my name on their schedule and then they’ll speak first and I just have to acknowledge.
I probably tell my name to people twice a month, on average. First name only. “Paul” is a universally common name with one syllable. No point in confusing anybody with unpronounceable surnames or weird nicknames (I’ve never really had a nickname).
I go by Emily, my middle name. It caused a lot of problems in school when teachers would first see my (first, middle, and last) name on the class list, and initially call me by my first name, and I’d have to correct them. I finally got rid of this problem when I signed up for university using just my middle and last names.
I usually just go by “Long Schlong McHugenDong”
I voted “other” - I go by my first name at work and with my family, but to most of my friends I go by my SCA name, since that’s how I know them.
Depends on the circumstance. The issue is not really what I call myself, but what others call me.
By friends and family, I am [firstname]. My name can be shortened, but I don’t like it, so when others shorten my name, I immediately correct them and never have to deal with that again.
By work colleagues and very close client contacts, I am [firstname].
By new clients and other business acquaintances, I am either Mr. [lastname] or Dr. [lastname].
By industry colleagues and whenever I give or participate in presentations, I am Dr. [firstname][lastname].
I had a nickname, but haven’t been called it since I was 13, and that was solely by family.
Missed the edit window…
By my wife, I am called either papi (which I have gotten used to) or babe (which I hate); she never, ever uses my real name, unless she is discussing me with someone unfamiliar.
If asked for my name, I usually tell people “Patrick”. Eventually, as people get to know me, they’ll often resort to “Pat”, and that’s cool too. Which do I prefer? I prefer “Patrick”, slightly.
For a short while in 4th grade, some friends started calling me “Andy”, which is short for my middle name. We moved that summer, and I’ve been “Patrick” or “Pat” ever since, not counting air-names when I was a disk jockey.
I’m confused as to the lack of multiple choice for this poll as I do first, last, and initials rather interchangeably.
There are a lot of us here. 
Maybe we should start a club!
I actually don’t care if I get called Julie vs Julia anymore, but since I insisted for probably 25 years that’s what I get, and it is always how I will introduce myself. I just recently found out the Great Grandmother I am named for was originally Juljanna, but changed to Julia when she immigrated to Canada.
Also EVERYONE I have met who is Russian (immigrant or permanent resident) or first generation Russian-Canadian either has a mother, daughter, sister, or aunt named Julia, or is actually named Julia. I could never find things with my name on it, growing up (always “Julie”) now I know I was just in the wrong country!
My brother calls me Jules, actually for a time he called me “Verne”.
I have a cousin named Julie, but she is younger and she got called Julie-middle name. Which is her mother’s name. Her mother who abandoned her at age 2. When my cousin and I got reacquainted in later years, she said it is only Mom’s side of the family that ever called me that, to differentiate the two of us. She goes by Joolz to almost everyone, and only Julie if she has to. NEVER the hyphenated version.
Missred My ICE plus all my non-governmental ID has Julia on it. I always say if I got a tattoo it would be “Call me Julia. I’m left-handed.” probably right on my CPR sweet spot. Or on a wrist.
I would almost bet that at least two of us have the middle name of Ann(e). 
And that we were born sometime between 1955 and 1965.