What nicknames do you call your animals that are not derived from their actual names? Please also tell us the actual name and what kind of critter you have.
Bruno (cat):
The Brown One
Kittle Kittle Blop (I don’t know why)
Dirtchin
Big Stripey Turd
Lloyd (cat):
Fattapuss
Stoopid
“Special” Kitty
Darlin’
Lilith (dog):
Doglet
Monkey Ass
Bitch
Pigdog
Doggalina
The dogs are Loki and Freya; both Boxers.
They are both refered to, individually and in the plural, as:
[ul]
[li]Butthead[/li][li]Knothead[/li][li]Moron[/li][li]Fuzzbutt[/li][li]Gruesome[/li][/ul]
Being Boxers, they don’t care what you call them so long as you have a happy tone to your voice.
Freya alone is occasionally refered to as Satan, which is actually a reference to a now deceased predecessor Boxer. They have much the same temperament.
One cat came to us named Boomer, but was once referred to as Booger and the name stuck. Maybe that one doesn’t count per the OP. The other cats I ignore as much as possible.
My cat Cuthbert is “The Boopalo.” I have no idea why.
All pets are occasionally “Skeezix.” But that’s because it’s a term in my family used affectionately. I also have no idea why.
Also: the cats, when they are being good together, are “the Little Brothers”. When they are rotten together, they are “Shittens”.
I’ve had a bad and then good past month with dogs. I had adopted an 11 month old french bulldog mix who died in his kennel after having him a month. 
Then I had a friend of a friend hear what happened and her dog just had puppies. So she gave me one, a cute little collie/spaniel/lab mix. Unfortunately the little guy gave me such an allergic reaction that the next morning I had to find a new home for him immediately. (Luckily that wasn’t a problem, as I knew a family that was looking for a puppy and now I get to visit him outside).
So, onto my 3rd dog. A black pug that was rescued from a puppy mill by a shelter. I named him Spoon.
He also has been called:
Puglet
Chooch (by accident as this was the first dog’s name).
Oinkers
All cats:
Havoc - Lump-Lump, BBW
Pixel - Assassin, Stinker #1
Caelan - The Orange Terror
Brindle - Chub-Chub, Stinker #2, Little One
My cat’s name is Marmalade
Nicknames include
Smoofer
Mr. Beggy Mc Beggarson
Whiskerface
Mr. Sheddy McSHedderson
Goddamn it, cat
This is funny, because I find that no matter what I name my pet, he/she is rarely called by that name. My last dog was named McRae, but I usually called him:
Mickey
Mick
Pookie
Smokey
Sparky
BooBoo
Buddy
Punkin
Mr. McRae
and probably other names
I’ve only had my present dog about a month. His name is Jake, but I call him:
Bubba
Punkin
Boo/BooBoo
Jakey
Jaker
and I’ll probably come up with other names as time goes by
As you can see, some of the nicknames have worked for both dogs
(Ahem.) An excellent choice of name! 
I don’t have a lot of names for my cats that are not derived from their proper names somehow, but there are a few. Tigger is often known as “His Royal Bigness” because of his size and arrogance. Denver, who is all black, is sometimes called “Inkpads,” because his paw pads are, well, black. And Shiloh, who has yet to vocalize a proper meow, is called “Meeper,” after the sounds she does make.
Kola, cat. Nickname is “Schpink”. A very long story, though it’s related to the lisp which Mooch (the cat in the comic strip “Mutts”) has.
Nijel the Destroyer (cat) is most often called Monster and sometimes Tank.
Mrs. Peel (cat) is known as Butt, becasue of how she is with the other cats.
Pearl (cat) has stated to be known as Betty, which is short for bete noir.
Milo has never been anything but Milo.
My cats are Jackson, Zachary and Simon and I find myself calling all three of them, at different times, “Baloney Sandwich” or “Tootsie Roll.”
Jackson’s also called “Handsome Man” or just “Handsome” because he is.
Simon is sometimes “Baby Boy” or “Pretty.” Simon really is pretty, I told him this morning he could be Miss America and I’d buy him a sash. He was ambivilous.
Zachary is a girl (I named her young, thought she was a boy), so she get’s called “Girlie” or sometimes “Jessica Girlie.”
Dog Sawyer = Nayla
Bobtail cat Muffin = Bob One
Bobtail cat Wilson = Little (though he is a huge cat)
Cat Booboo = Mr. Bodinsky
All the others are mutations of their actual names. Muffaletta, Muffalopolis, Rufus Rupert Magoo, April May Kitty Kitty Kitty and so on (2 dogs, 5 cats)
Cinnamon the dog. Called Dude most often. Although he’s sometimes Tardo. Or Tardo McWoofwoof.
We have three cats… one’s original name is Snickers, but she is now known as Blobby because of her fatness. Actually, that’s practically become her official name.
We also have a dog, Ginger, whose nickname is Dubbers. This is a term my daughter coined; it sort of means a smallish dog.
I have two rabbits, so I usually nickname them boring things like:
Bun-Bun
Mr. Bun
Bunny-Boo
Fuzzbutt
Furball
Big Ears
I also call them Mr. Cottontail and Mr. Coaltail, as the one with black fur doesn’t have the white “cottontail” underside to his tail.
Isn’t Bruno from the German word for Brown?
It is! And Lloyd is Welsh for “gray”, at least according to the baby name book I had at the time.
Most of my pets get called other things such as pooh-buns, honeybun, snookums or versions of their names with “poo” on the end. Only a few have nicknames specific to them. My cat, Pi, gets called stuff like Boogerface and Darth Sniffles, he has a chronic snotty nose. Sometimes I call him Popeye, which was actually his original name. Luna the cat gets called LooneyToons. The dog, Maggie, often gets called Maggot, especially when she’s being naughty.
Julian the cat:
Lumpimus Maximus
Doofy
Stoopy
Fuzzwad