You’ve reminded me that I knew a Miffy. Real name: Meredith, but Miffy to everyone. Sadly passed away at a young age for reasons unrelated to her name.
I’ve known a couple of Butches, MANY Bubbas, one Skeeter, and two Boogers.
One of the Boogers was a girl on my little league softball team. I’m sure she had a proper name, but I never knew it. She got pregnant at 13 and I lost track of her.
I went to high school back in the '80s with a Spike.
My wife had the nickname “Biff” as a kid. Short for Elizabiff. 
As I’m going through this I keep saying I know one of them. Could just be the hippie/biker lifestyle but I know or have known a lot of people by lots of nicknames. Some kinda common and some kinda obscure but most quite fitting once you know the person and/or the story behind the name. I’ve even thought I was hearing about two different people before finding out someone’s nickname/real name. And once when talking to someone discovered I was relating a second hand story about him because I knew him only by his nickname.
I have a distant relative I only know of as “Butch”; not sure if this is a given name.
Also know of a guy who uses the first name “Tiger” professionally which is all he has been called since elementary school.
I know someone named “Tiger.” It’s his given name, not a nickname.
I recall this one oddball who insisted on being called Cooter once The Dukes of Hazzard became popular.
I don’t; neither does my friend Muggsy. His wife, Cookie, concurs.
I know a Moose, he is 6’6" (or more). They nicknamed his smaller younger brothers Caribou and Elk.
^
Must be looks rather than size. 
I know a Lefty and a Moose. Also Butch, Bucky, and, Shitty. I remember my mom asking my brother what Shitty’s real name was. He didn’t know. It’s 20 years later and I still don’t know. Ran into him last year and the name embroidered on his coat? Shitty.