"Dammit, Sherlock!"

"You'll make Mummy very upset."

Introducing Mycroft!

Also, to avoid any confusion about who's speaking I'm going to code the characters:

Mycroft = bold

John = italics

Sherlock = normal

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"You'll make Mummy very upset."

"I can't go Mycroft! Like I said, I'm working on a case."

"Come now Sherlock, that excuse is starting to get old."

"You're telling me."

"Ah, hello John. I didn't see you come in."

"Oh I'm sure you did Mycroft. Anyway, why are you here?"

"Blunt as always aren't we?"

"You're telling me."

"Shut  up Sherlock."

"You two bicker like an old married couple Anyway, it's Mummy's birthday this weekend and she's more or less demanded that Sherlock and I go down to see her."

"For the whole weekend?"

"Yes."

"Sherlock, you're going."

"What?!"

"Someone obviously doesn't want you to stay here, Sherlock. Not that I blame them."

"I can't see why."

"Sherlock, you came in yesterday covered in blood and carrying a harpoon!"

"I explained to you why!"

"That doesn't make it any better!"

"Sherlock, your wife has spoken you must come to see Mummy."

"What?!"

"I can't Mycroft! And besides, I haven't got her anything."

"Why am I the woman in this relationship?!"

"That can be easily sorted my dear brother."

"In fact, we're not even in a relationship!"

"Oh, you shouldn't Mycroft. I wouldn't want to cause you any trouble."

"And if we were, I'd definitely be the man!"

"It's no problem. Can't have you missing out on the family dinners, can we?"

"No one's listening to me are they?"

"Definitely not."

"... I'll go and put the kettle on then."

"Splendid! I'll tell Mummy that you'll be there then."

"Wonderful..."

"Two sugars for me, please John."

"Sod off, Mycroft!"

"I've got him well trained, haven't I?"

"Indeed."