Does ANYONE understand what he's talking about?

Sometimes the Doctor does the strangest things while he's talking. Once, he explained to my brother (very slowly, with pauses between all the actions he named) how he was making his burger, and made the motions of making the burgers with his hands (such as putting them together and opening them out for cutting the bun, and flicking his fingers for putting on pepper). It was so strange it made me laugh, and I said, "I like the actions!" At first, he didn't know what I meant, but then he realized, and, meaning every word, said, "It helps me to understand what I'm saying." This reminds me a lot of "The Ark In Space", when the Doctor starts talking to himself, and Sarah explains to Vira, "He talks to himself sometimes because he's the only one who understand what he's talking about", which, by the way, the Doctor I know also does very frequently.
Sometimes, though, I'm not sure even the Doctor understands what he's talking about.For instance, we were driving in the car, and I said something like, "It sure is dark!" Then he said, "No, it's not dark, it's just less light." That really makes me think of "Pyramids Of Mars", when Sarah tries to show the Doctor the door, but it isn't there, and she says, "It's vanished!" to which he calmly replies, "Nonsense! It can't have vanished! It's just disappeared. That's all!" And according to my dad, he once answered a phone call at work, saying, "Good morning - I mean, good afternoon. What question do I have for you today?" Somehow, I don't think this is the normal way to answer work calls. He even said the same "Good morning - good afternoon" thing to me once when he came home! I'm not sure when, but I remember the Doctor of the '70s TV shows saying something that was similarly complete gobbledygook. It's things like this that really prove to me that he's the Doctor. I mean, who else could say things this ridiculous and still be perfectly normal-looking when he has to? (Well, half of the time he has to...)