The smile plastered across Sherlock's face couldn't look phonier if he were actually trying. John elbowed him gently in the ribs, hissing through his teeth.
"Smile, damn it. They're trying to thank you."
The fake grin widened, all shark teeth and cheekbones, as Sherlock shook the businessman's hand.
"Thank you so much, Mr. Holmes, you've saved us from bankruptcy."
"Embezzling is such a pedestrian crime. Anyone could have figured this out."
John glared sidelong at Sherlock. "He means thank you."
Thankfully, the man was too pleased with the outcome of Sherlock's investigation to be concerned with his lack of manners. With a flourish, he pulled a long, narrow box out of his suit pocket and offered it ceremoniously to Sherlock, who eyed it with distaste. Smiling gratefully, John accepted the box and proffered another thank you.
In the taxi on the way home, Sherlock fiddled with the box, not deigning to even open it.
"A fountain pen, John. Have you ever seen me with ink on my fingers, or my cuffs? What reason would they have for buying me a fountain pen?" He shook the box, causing a substantial thump. "And an expensive one, at that. Probably a Montblanc. I'll give it to Mycroft, he's a sucker for the trappings of wealth. I'm much more comfortable with a sensible old biro."