Rolling Stone has a good, longish Q&A with Charlie, in which he talks about Anomalisa, working in customer service, the weather, and this:
I took a stop-motion animation class in high school[...]. I did one three-minute animation with clay, about an artist working with ... a big piece of, I guess, clay. And I built a loft studio out of a cardboard box. It had a skylight and a pipe going up the corner. He was sculpting this mound of whatever it was, and it started to come to life. The concept was pretty basic: The thing came to life and it started turning into all these different things. At one point, it threw him against the wall. I didn't know what I was doing, but I got him off the ground by having little toothpicks under his feet and I shot it from an angle where you couldn't see them. It was clear he wasn't touching the ground as he was being thrown, and I was really proud of that.
Then one of my teachers wanted to show it in his class: I had one copy and he lost it. I was really upset, because of the movies I made as a kid, this was the most accomplished and it was the thing I was the most proud of. I was so clear that I gave it to him and he was so clear that he gave it back to me. And the fact that a teacher was, in my opinion, lying to me to save face as opposed to taking responsibility, it was just really creepy to me. (Source)
What an ass.