"The Art of Mind Over Matter" joke

A young Army man who just completed a year tour in Alaska, unaccompanied, had finally returned home.
The first night he was home, he excitedly said to his wife, "Honey, I want you to know that I didn't waste all the time I spent alone. Instead, I mastered the art of mind over matter. Just watch this!"
He then dropped his trousers and shorts and stood before her.
"Now, watch closely," he said to his wife. Next he said, "Dick, ten-HUT!" With that, his dick sprang to full erection. He then said, "Dick, at EASE!" Immediately, his dick deflated.
"That's amazing!" exclaimed his wife. "Is it all right if I bring our next-door neighbor over to see this? This is really incredible!"
Being so proud of what he had accomplished, he told his wife he didn't mind at all.
She quickly went next door and returned with a gorgeous looking woman who immediately got his full attention. After a short pause to 'compose' himself, he said, "Now watch this." Then he said "Dick, ten-HUT!" and his dick sprang to life.
Next, he said, "Dick, at EASE!" but nothing happened. He repeated the command, "Dick, at EASE!" Still, nothing happened.
Embarrassed, he ran off to the bathroom. His wife promptly made excuses for him and rushed off to join him in the bathroom. When she got there, she was shocked to find him masturbating.
"What in the world are you doing?" she asked.
"I'm giving this son-of-a-bitch a dishonorable discharge!" he said.