A few months before starting college in was in a pretty serious auto accident that left me with a large scar on my face. My new roommate decided that I looked liked a dinosaur (specifically, the pet in the Flintstones). For the next four years I was “Dino” (pronounced ‘Deeno’) to everyone I knew at school. I don’t think many knew that it wasn’t my given name.
A (now long-dead) relative was named Francis, but was invariably known as Doug, as he had once had a Douglas motorbike.
An Indian colleague was named Rohail, but invariably known as Rollo, and if anyone called asking for him by his real name it was a sure sign that they didn’t know him.
When I was 7, I was inspired by the nursery rhyme “Georgie Porgie, pudding and pie / Kissed the girls and made them cry” to go up to random girls at school and kiss them. (Just one of many antisocial, limit-testing things I did at school at that age). Besides getting me in trouble and prompting my parents to throw out the book that contained the nursery rhyme, it earned me the schoolyard nickname: the Kissy Killer.
When my daughter was in kindergarten, a boy in her class was called Kissy Boy because he kept trying to kiss all the girls. By the time they got to high school, he’d gotten over it and was a quite pleasant young man. 
I wore sports goggles in high school gym class, so a couple of bullies called me “Goggles”.
As a young kid I worked in mum’s cafe after school and on weekends. With white blonde hair and skin that wouldn’t tan, the teens who inhabited the games room christened me Casper the friendly ghost. That stuck with that group forever. I bumped into one in the local pub 30 years later and he’s like “Hey Casper”
Around the same time I got my School nickname which was Goober. NFI how it came about, one guy a year older christened me one day and it stuck, right through high school.
Nowdays I’m just Stui or Stu.
I can’t say the actual nicknames because it would make it easy for anyone who knew my family to identify me but my brothers and I were given nicknames by our hockey coach. None of the nicknames were related to our real names. Instead they all followed the same theme (which I also can’t say). I’ll substitute a different theme to illustrate how the theme worked.
I had twin brothers. They were Cake and Ice Cream (because they go together). I was Cookie. My other brothers were Brownie and Jello.
My brother did. His nickname is “Tony”, which is pretty standard for someone named “Anthony”. When he was in high school, however, his nickname was “Bomber”.
He got that nickname because of high school football. Like a lot of rookies, he started out on special teams. He would hit people so hard that the sound was clearly audible in the stands. His fellow players likened it to a bomb going off, so the noun nickname “Bomber” evolved from that.
My dad used to call me “Blue”, because of my eyes. Both of my parents had brown eyes, as do my brother and sister.
I served in the army with a number of guys with nicknames that were unrelated to any of their names, most notably a guy called “Joe Emerald”, the only person I’ve ever met with both a nick-first-name and a nick-last-name, neither of which were in any way related to his real names - making it more of an alias than a nickname, per se.
At one point more people knew me as “Frodo” than my real name, we met to play RPGs all night every Saturday from '96 until about 2002, I met them through a BBS were my username was “Frodo” so they called me that, with time most of my friends were from that group or people I met through that group so they also called me Frodo.
No, not that one, but his real first name is Dave…
I won’t call you Cookie if you don’t call me Cake.