The Doctor always figures that one of his good qualities is that he's able to get along with pretty much anyone. Sure, there are people he likes more, and people he likes less than others, but in general, he's not an unsociable person.
However, for some reason, he finds that whenever he spends time with the Master, there comes the point when he would gleefully use the sonic screwdriver to poke the Master's eyes out without feeling a hint of remorse.
"Stop that already," he says, his tone bordering on a hiss, and swats at the Master's fingers as the Master starts playing with the TARDIS controls yet again.