Tell Him I'm Not Speaking to Him

A scene with (at least) three characters present (Alice, Bob and Carol). Alice is refusing to talk to Bob for some reason, so she repeatedly says to Carol, "Please tell Bob...". There are a few variants on this:

Bob sometimes replies directly, sometimes also via Carol.
Carol sometimes actually repeats what she's been asked to say, sometimes doesn't bother.
If it goes on long enough, an exasperated Carol might tell Alice to tell him herself.

Examples of Tell Him I'm Not Speaking to Him include:

Literature

Granny Weatherwax and Magrat put Nanny in the middle in Witches Abroad.
In Thomas Costain's novel The Black Rose, Walter's grandfather has made an oath never to speak to him (does anybody remember why?), and always speaks to him via his mother. Near the end, though, he accidentally addresses Walter directly three times, and decides the oath is permanently broken.
Happened between Harry Potter and Ron, with Hermione in the middle (third or fourth^{[please verify]} book and movie).

Live-Action TV

Happens to Elliot twice in Scrubs - in one episode Dr Cox gets annoyed with her for deliberately setting him up to say the wrong thing to a German patient, so when she asks him for help, he talks to a stapler. And for much of Season Six, once she becomes "Private Practice Barbie", Dr Kelso refuses to aknowlege her existence, and talks to her through the nurses.

Web Comics

In this Something*Positive strip.
Spacetrawler has a variant where it's less about refusing to speak, and more about recruiting the third party to bolster their argument, and the third party is an Extreme Doormat.

Nogg: Cardinal62. Tell them we're the good guys.
Cardinal62: (To Emily) We're the good guys.
Emily: Well, tell alien-fish that I know a dozen good seafood recipes he'd go lovely in.
Cardinal62: (To Nogg) She knows a dozen good seafood recipes you'd go lovely in.
Nogg: Well, you tell her that-

Western Animation

In Dr. Katz, Professional Therapist, Dr Katz talks to Ben via Laura after Ben bought a huge TV.
In The Simpsons, Homer and Lisa talk via Marge/Bart when Lisa ruined Homer's barbecue in "Lisa the Vegetarian". (Homer soon gets confused about who he is/isn't talking to).
In Doug, the breakup of the Beatles homage band The Beets plays out like this, with all four members of the group facing away from the microphone and saying things like this ("I'm not telling them, YOU tell them!") before one finally has enough and very curtly says that they're splitting up.
Shaggy and Scooby did this throughout an episode of A Pup Named Scooby-Doo, using Daphne as an intermediary.