Hopefully it's not a slur...

Who are you and how did you get in here!?
- I’m a locksmith and I’m a locksmith.
Your name is Lizardman Lizardman?
- Well, if you have just 1 name, then technically, it's your first, middle, and last name at the same time
- Wait until you find out about the Mario brothers.
- The captions are off, originally it was, "Name, race, and occupation?" It was the only picture I could find, though.

You're a mean one, Mr. Grinch.

So likely his name, possibly only his last name.

Maybe that's meant in a derogatory way though
- The entire song is derogatory. If you sing, "You're a butthole, Mr. Stinky", then you haven't identified who you're singing about, unless someone is actually named Mr. Stinky.
Full name Chauncey Tiffany Grinch.
Yes, his first name is Ethan.
- Not Elon?

‘Grinch’ is a holistic integration of multi-categorical nomenclatures.

Im going to use that on my friend who works in HR

He's not a who, he's a what

Which is why
High in the sky 
The Grinch didn't like Whoville very much
Every one was so-and-so, someone or such

https://m.youtube.com/watch?v=7XduYIKu20Q

It’s a title, like village idiot.

or the village bicycle
- Keep my wife's name out of your goddamned mouth!
- or the village rapist

I can't find a specific image of it, only a reddit post talking about it, but in Grinch (2018) he buys green hair dye. I interpret that to mean he is just a normal whoville resident, but dyed green. I suppose his green grinch hair could be graying and he wants to look young, or he could just be some other color and chooses to be green, but I like to imagine him as some crazy naked hermit that makes himself green and everyone else just puts up with it.

I don't buy it. Anything beyond 1966 is not canon in Dr. Seuss' The Grinch-universe.
In Dr Seuss' How the Grinch Stole Christmas (2000), he was green since the day he ~~was born~~ drifted in on his pumbersella.

It's most likely either a species (like the sneetches) or, to my mind, a descriptor given to him by the narrator. Keep in mind no character (namely the grinch, who does speak) ever refers to himself as such. Sort of like if someone narrated your life and called you "the grouch".

It's a personality.

It's a lifestyle choice!
- Like his decision not to wear pants?

Yes

I thought it was a character trait. I assumed he had a "Who" name, but no one uses it because he was being a dick all the time so they called him "the Grinch."

Sorry, going to be that person https://www.etymonline.com/word/Grinch

Grinching wouold be a nice new slang term.
- Grinching – the opposite of gooning.
  
  "Yo fam you wanna go gooning later?"
  
  "Nah I'm hard grinching rn fr fr"
- Really grinched it for the win

His full name is Ethan Grinch

https://seuss.fandom.com/wiki/The_Grinch#%3A~%3Atext=His+full+name+could+be%2Cby+Camilla+and+Rose+Who.

Yes

Grinch is s state of mind

He's Mr Grinch, so it's at least his last name (and also explains him being THE Grinch who stole christmas). It's possible that it's also his job (see "Smith"), but prefer that grinching is named after him, a la Scrooge

It's his title, short for Exalted Grandiose Grinchimus Maximus de la Biblioteca.

All of the above.

it's a nickname

https://en.wikipedia.org/wiki/Gringo