Carrie: First of all, l'd like to thank all of you who've flown in from the States. I'm really touched. As for the rest of you, l'd have thought that lots of frightful Americans flying in was an excuse for staying away, so I thank you, too.
Tom: The great advantage of having a reputation for being stupid: People are less suspicious of you.
George the boor at The Boatman: I was at school with his brother Bufty. Tremendous bloke. He was head of my house. Buggered me senseless. Still, it taught me about life.
Answer: A groom can choose whoever he wants as best man. As you say yourself, it's by no means mandatory for it to be the groom's brother, even if they are close. In this particular case, it's possible that David felt that he ought not to be the best man, due to the difficulty that he'd have in making a speech, but, really, Charles was under no obligation to choose him.
Tailkinker ★