There's a scene with a trans lady, that goes something like this:
- Knock on door
- Lady walks in: "Ah, Coop!" (greeting agent Cooper)
- Cooper: "Dennis?"
- Lady: "It's a long story, but actually I prefer Denise if you don't mind."
Usually when I see a trans lady in mainstream shows, I'm expecting her to be the butt of the jokes. Some of the side characters are a bit taken aback and transphobic, but Agent Cooper (arguably the main character) just takes it in stride that his colleague is trans.
I wasn't expecting anything that could be considered "progressive" in Twin Peaks, so a relatively-well portrayed trans woman is a very pleasant surprise. She has a deep voice (she's played by a cis man) which might have been meant for humor but from my modern evil SJW eyes, I just see some rare and rather good representation.