It's not... a slur, is it?
Grinch was the scientist, but the character commonly called “The Grinch” is really Grinch’s monster, created by Grinch.
Or maybe he’s like the Hulk and turns back into a regular Who when he’s in a better mood?
Is that why he’s naked? His regular clothes are too small when he grinches out?
This theory is making more and more sense. Which also implies there’s no Who Tony Stark to make him the uber-stretchy pants.
Too large by three sizes. His transformations start with the heart.