You had to be more than a little crazy to be one of the early astronauts. Your job was to bronco ride one of the biggest bunch of explosives known to mankind. Lest we forget, when NASA started out, it was definitely playing catch-up to the Russians. The US space program began with a string of very public and very spectacular mishaps, all of which led to the saying: theirs go up and ours blow up. So having a screw loose was a prerequisite for the space program. Then on top of that, you had to add in a dash of test pilot and warrior mentality. It must have driven the bureaucrats nuts, and I know Pete Conrad did.
The man was bright. Heck, he had a degree in Aeronautical Engineering from Princeton. But like many of the early space jockeys he thought all of the psychological testing he had to do was not only demeaning, it was utterly worthless. So the man who once when asked the secret of his success replied, "if you can't be good, be colorful" not surprisingly rebelled against the strict NASA protocols. My favorite story may be about the time he was shown a blank piece of paper as part of a Rorschach test and told the psychologist that it was upside down. Being a bit vertically challenged myself, I also like what the 5'6" Conrad said as he became the third man to set foot on the moon during Apollo 12: "Man, that may have been a small one for Neil, but that's a long one for me."
NASA knew it had a winner with Pete Conrad. He truly had all the right stuff and the public loved him. The biggest problem they foresaw on his moon mission was that, in keeping with his personality, he had a penchant for rather salty language. And that is a big problem when your every word is broadcast to a few billion people. So the rumor is that they came up with a novel way to keep Pete from slipping up (or down). They hypnotized him and told him to hum every time his mind was wandering so he would not accidentally let out an expletive. Technically, NASA has never admitted that they had him hypnotized. However, they have admitted to using the tactic. And if you want to go listen to the Apollo 12 tapes, you will find only one astronaut merrily humming for whole mission: Mission Commander Pete Conrad.