When I adopted Loki in December, they had named him Speedy. While I thought that name would be cute once he was old and fat, I couldn’t keep that name since I had already had a turtle named Speedy when I was a kid (I’m not kidding, he was the fastest turtle I’d ever seen). For some reason, I didn’t feel like I could have two pets with the same name. After about a week, I decided on Loki. He’s really taken a liking to that name it seems, and is becoming more mischevious by the day. And I wouldn’t have it any other way.
I’ve been kicking myself lately for naming my kitties Lloyd and Bruno…ever since intuiting that their actual names should have been, respectively, Nocturnal Bastard and Stripey Piece of Shit.
No, Thanatos was orange. But Punkin was taken. 
Actually it was taken in a past-tense kind of way. I had a Punkin when I was younger, and he was one badass mofo: six-toed and all muscle, undisputed king of the neighborhood. One of my favorite cats ever. Anyway, the name Punkin has been retired in my world, unlike Blacky, of which I think I’ve lived with 5 or 6!
When we went to pick out our oldest kitty at the pound, his name was Quincy. We named him Mr. Bigglesworth but have never called him that. His name’s Poopy. I call him Focker sometimes.
When our second cat came along, my husband insisted that we name him Pants, to go with the Poopy. I liked to call him Sir Pantsalot.
Then we got our third. He was so tiny and cute I said he was cute as a bug’s ear. He came to be known as Bug or Buggy. I call him Mr. Stinky or Stinky McTwinkletoes sometimes.
Then there’s the dog. His previous owners named him Chico. My husband wanted to name him Kyle or Henry. I named him Weezer. The only bad thing is that people think it’s Wheezer because they don’t get the band reference. Oh well.
Our poor animals probably all think their name is Who Are You? I get mad at one and start to yell and can never get the right name out first. It usually comes out sort of like, “Poo … Buh … Puh … who are you!”
We’ve renamed a couple of pets. We had a cat who’s real name was Cuddles (named by my sister who was about 7 or 8 when we got him) that we called “Jabba the Cat” due to his extreme girth. He learned and responded to that name.
My parents also have a pair of cockatiels who have sort of renamed themselves. They individually have real names, but they don’t respond to them at all. They seem to have decided on their own that their name is “Hi Guys” and they collectively respond to that (although there are two of them, they always stick together and are basically one entity). Everyone just calls them The Hi Guys now.