"What are you doing with that? That's highly personal. You can't touch it."
Rose Tyler looked up at the sound of the Doctor's voice. "You've let me use it before."
"Well, yes," he admitted, "but those were circumstances of life and death. Please just put it down. Gently!"
She looked at him like he had lost his mind, but gently set the sonic screwdriver down. "There."
"Thank you," he said, looking relieved.
"Now why can't I use it?" she asked, crossing her arms. "I mean, I actually wasn't really doing that much with it. I was just…looking at it."
He sighed. "It's just that it's my tool. I don't like it when people touch my tool."
She raised her eyebrows. "You don't like it when people touch your tool."
"You can understand that, can't you?" he asked. "It's important to me. A Time Lord's tool is one of the most important—"
At that point, Rose lost control of the giggles she had been holding back and began to laugh out loud.
"What?" the Doctor asked, looking offended. Rose laughed even harder. "What? Rose, what? Did I say something—"
Then his face fell with recognition, and he shook his head.
"You humans have such filthy minds," he muttered. Rose kept laughing.