The grin flashed again, just for a moment. "Always get in trouble when I do that, me." And he got in enough trouble on his own. Donna'd kill him if he started drinking again. And, of course, there'd be that disappointment in himself. He hated that.
Though the 'trying to be nicer' thing didn't always work. All these humans running around asking stupid questions all the bloody time... "Right. So. This is my ship, like I said, yeah? She's called the TARDIS, that's Time and Relative Dimensions in Space. I'd explain how it works, but your mind wouldn't be able to grasp a word of it."