There’s supposedly a scene that was cut from the first episode, that after Wardog introduced himself as “The Wardog”, Probst turned to Rick Devens and asked his name. Rick replied “This is kind of embarrassing, but my name is also The Wardog.”
Yeah, this. There’s nothing remotely weird or affected about ‘Cat’. One of my best friends is Cat, and she’s a partner in a law firm.
Cat, Kate, Katie, Katy, Kath, Kathy, Cathy, Kay - all are perfectly average and acceptable diminutives of Catherine/Katherine. My first name is Catherine, but you’ll get stink eye from me if you use it (I also don’t go by Cat, for clarity’s sake).
One of my closest friends has a daughter whose name is Lily. Everyone always called her Lily. When she was 16 or so, she said that she wanted people to start calling her “Kat.” I privately thought it was a little affected, but I went along with it, while secretly rolling my eyes at the weird pretensions of teenagers.
About six months later, I remembered that her middle name is Katherine, and realized that she was just letting people know that she preferred to be called by her middle name rather than her first name. Made me feel pretty silly for being so judgey about it.
I work with a Samuel, tho he goes by Sam - I think he’s about 25… I don’t think it’s all that unusual a name.
So, uh, no “JT”?
I have a sometimes drinking buddy named Bill. Pretty common name, so when I asked a bartender if she’d seen Bill lately she asked which Bill I was talking about. I described Bill and she said, “Oh, Dollar Bill”.
Turns out my friend’s nick (behind his back) is derived from the fact that he always tips a dollar, regardless of how much he drinks. I had no idea.
Recently, the surfer “Tubesteak” Tracy passed away. When I retire I may adopt that moniker
Now that’s a nickname. Love it.
I have the best nickname story of all! And crossing heart it’s true!
I think the guy is a second cousin… when he was born, his father named him “George John.”
Mom didn’t like that name. She called the kid “Tommy.” All throughout his childhood, all the years of school, he was known exclusively as “Tommy.”
Tommy grew into a fine young man, and he fell in love, decided to marry. His fiance was discussing wedding plans with her father, and Dad was ordering the invitations.
“I need to know if his name is Tom or Thomas.”
Bride to be says, “Neither one. There’s a funny story about that…”
~VOW
I’m with you on Mimi (and Cat, for that matter). I work with a 50-year-old woman whose prefers the nickname Mimi. I just can’t do it in a professional setting. Always seemed to me to be a good name for a stripper.* As for people calling their grandmother Mimi, I’ve never encountered that one.
*Just my opinion. No offense intended to anyone on the Board named Mimi.
Well, if we’re telling stories now…
My dad, a William, used to go by the nickname Billy. This lasted as he grew up, got a job, worked in an office, became project leader, and so on. I was named after him, including the nickname.
Sometime when I was around three, maybe four years old, I announced at dinner one night that I was too old to be called Billy, and would be thenceforth called Bill. I was quite firm on the subject and thus was my nickname changed.
My dad decided to change his nickname to Bill that same day. 
My father was nicknamed “Tootie” by his grandmother when he took trumpet lessons for six weeks when he was a kid. When he died, we had to put “Tootie” in the obituary because very few people knew that his real name was Lewis.
I am Mrs_Ducky because my husband’s nickname is Ducky from his days on the railroad. Everyone had a nickname and his was derived from his first and middle initials D. L. They started out calling him “Duck Lips” and eventually dropped the “Lips”, and now he goes by Ducky. His dad was also on the railroad and his initials were M. L. Although transposed, they called him “Elmo”.
Happens more than you might think. I have a best friend whose name is Herbert, but he always goes by Ron, even though there’s no Ron anywhere in his name.
My own mother was named something similar to Myrna Hester Smith, but she loved the book Pollyanna as a child. She started insisting that everyone call her Polly. This went on for over 80 years. When she passed away, people were shocked to find out her actual name.
My cousins’ grandfather (on the side not related by blood to me, which is why he wasn’t my grandfather 
) went by Schatzie (German for “sweetheart,” as I understand it). Like your father, very few people knew his given name (I knew it at one point, and have long since forgotten it, since no one ever used it). He lived in a small town in Wisconsin, and had even gotten the local telephone company to give him a second listing in the white pages under “Schatzie,” because he was well-known in the town, but a lot of people didn’t even know his last name, either.
Holy F, that’s pretty damn funny. I would almost have to call him that for the pure comedy of it all.
Spanish death notices often include any non-obvious nickname in quotes, either between given(s) and last(s) or at the end. She’d be listed as:
Myrna Hester “Polly” Smith
or as
Myrna Hester Smith, “Polly”
Just by its existence, that custom indicates how common it is for Spaniards to have a non-obvious nickname. My brother Ed has a ton of nicks and half of them are non-obvious. I’ve actually received calls where the caller couldn’t remember his name, started hemming and hawing… “you want Crazy Wolf or The Accountant?” “Uh, Crazy Wolf. Thank you!” “EDUUUUUU! It’s for you!” (Jay wasn’t an accountant, and in fact is not an accountant but a comptroller, but he’s been all about numbers since he was a little kid).
I knew a guy who had been named “Henry Louis” after H.L. Mencken, but when his parents found out that Mencken had made anti-Semitic remarks they started calling him “Jack” or some other unrelated name. That’s how he was known the rest of his life.
I had a co-worker who said to call him Big Baby. I just could not do that.
I have an acquaintance that is called Monster, he is about 6’7" his shorter brother , about 6’3" was called Shorty. I have no idea what their real names are.
I had a friend who took on a nickname as an adult to avoid confusion at work. his new friends used the nick name, his old friends used his real name. No changes in rotational speed of the planet occurred.
We asked him if it mattered and he said no so we did our due diligence.