It's a short fiction story in which a scientist was abducted by aliens and taken aboard their ship. The aliens wanted to know whether humanity was worthy of continued existence or not, so they took "the best sample" — a scientist — and conducted mental experiments on him, such as putting him through mazes and giving him erotic journals, in order to find out.
Initially, the man passed the tests, but then he started to get angry, feeling like a rat in a maze (he himself conducted experiments on rats), and began to do creepy things during the experiments, intentionally failing them. The aliens couldn't understand why he was doing this, but decided, based on this unknown behavior, that all of humanity should be destroyed.
I read this 12-15 years ago and I think this story was written in 50s or 60s — the golden age of American fiction stories. The story was both humorous and sad, with a lot of thinking by the captured scientist.