Cardboard against cardboard.
Styrofoam against styrofoam, or anything against stryrofoam.
Fingernails against drywall.
But the absolute worst is…
Fingernails on a car.
I can’t take it. I get lightheaded when I hear it. In the movie U-Turn, which I don’t recommend anyway, Billy Bob Thornton scrapes something metal against the hood of a car, and everyone in the audience started losing it. Another reason not to see it.
Oh, I thought of another one. I was in a used bookstore, and discussing with the owner the possiblity of his doing a book search for me. During this, he started cleaning his pipe with a knife, and got just the right angle against the wood to make the most horrifying screeching sound on earth. He didn’t understand why I was making those faces, or why I finally ran outside and waited until he was finished. They say you can’t make a noise to annoy yourself…
Remember, I’m pulling for you; we’re all in this together.