"It is an established pattern, John, that a greater genius will often have more prominent… foibles. I myself endanger my life in the pursuit of puzzles, Mycroft steals umbrellas. We all have our own idiosyncrasies."
"Sorry, Mycroft what?"
"Oh, haven't I brought that up in your presence yet? I must have been in a good mood. Mycroft pinches umbrellas. Has done for years. That's why he always carries one of his own about, so that if he gets caught he can always say it was a mistake, and it's not so awkward when he has to return it to the owner if he doesn't."
"I imagine he gets away with it more often than not. "
"Well, naturally. He is a Holmes, after all. I believe he's stolen one cabinet minister's brolly three times."
"Wow."
"I used to plant brightly coloured ones in places I knew he'd have to visit, just so I could see him carrying one of them around later. It was great fun on rainy days. I used to put one in every room of a building and watch to see which one he would be forced to use when he came out. There's a whole photo album somewhere under that analysis of stamp glue."
"You're a cruel man, Sherlock."
"Merely sportive, John. After all, we are brothers."