The first time I ever saw A Study In Pink, the two-pill situation reminded me so much of the iocane powder scene in Princess Bride that I just had to combine the two. The scenarios aren't exactly the same so forgive me for changing it a bit. :-)

I did my best with the cockney. Sorry if it's confusing.

Am I really the only one who made this connection?

The two men faced each other across the table, each waiting for the other to move first. The still air in the dimly lit classroom belayed the tension, as both stared at the other with narrowed eyes. Between them sat two glass bottles, each containing a single pill.

The cabbie's cockney accent finally broke the silence. "Are you ready to choose, Mr. 'Olmes?

Sherlock dropped his analytic gaze from the cabbie to the bottle before him, and then to the one before his opponent. "This is ridiculous," He mumbled, but the look in his eyes was that of insatiable curiosity.

This didn't escape the cabbie. "Ridiculous…and yet you're still 'ere." He leaned forward in a taunting manner. "Let me 'elp you. All you 'ave to do is divine what you know o' me: am oi the sort o' person 'oo would put the good bottl' in front o' me, or in front o' moi enemy? Now, a cleva' man would put the bad bottl' in front o' 'imself, 'cause 'e would know that only a great fool would reach for what 'e is given. You are not a great fool, so you can clearly not choose the bottl' in front o' you. But oi must 'ave known you were not a great fool, oi would 'ave counted on it, so you can clearly not choose the bottl' in front o' me."

Sherlock's eyebrows had come closer together with each sentence, and now he was blinking at the cabbie in pure disgust. Then he gave a deep sigh. It was exhausting to be in the company of idiots. Proper genius my arse, he thought. "You really like to hear yourself talk, don't you?"

The cabbie gave him a nefarious smile. "Oi'm just getting started."

Sherlock settled back in his chair with a groan, which went completely unnoticed because of the monologue going on across the table. He felt slightly like the bat he kept on his mantelpiece: pinned in place (though he had to admit that his own inquisitiveness was the pin), unable to escape this severe form of torture.

"Oi'm a criminal, Mr. 'Olmes, so o' course oi got criminal connections. Your fan, for instance. How else could oi have gotten a pill this deadly? Criminals are used to 'aving people not trust 'em, as oi am not trusted by you, so you can clearly not choose the bottl' in front o' me."

Another sigh. "Truly, you have a dizzying intellect." Sherlock was, at this moment, wondering if he should just choose and get it over with. It would be a win-win situation; no matter which pill he ended up with, he would be free from this vexatious rant.

"Wait till oi get going! Now, where was oi?"

Sherlock pressed his lips together with a sharp exhale. "Criminals."

"Yeh, criminals. And oi would 'ave suspected you would 'ave known where oi got the pills, so you can clearly not choose the bottl' in front o' you."

"Now you're just trying to confuse me." The detective said. "It won't work."

"It 'as worked!" The cabbie cried. "You 'ave no idea where the bad bottl' is!"

Sherlock sighed in exasperation and stood. "I'm finished here. I look forward to the court case." He gave the cabbie a condescending smile and headed for the door.

"Just before you go, did you figure it out? Which one's the good bottl'?"

Sherlock halted. He knew he should keep going, but he just couldn't. "Of course. Child's play."

He was bluffing, and the cabbie knew it. "Which one then? Which one would you 'ave picked, just so oi know if oi could 'ave beaten you." He jerked his head towards the table, a dangerous twinkle in his eye. "Come on. Play the game!"

Sherlock turned, unable to resist the challenge. He walked back, and with only a slight hesitation, grabbed the bottle in front of the cabbie.

"Ohhhh, interesting." The cabbie purred.

Sherlock opened the bottle and shook the pill into his hand. He stared at it, weighed it, sniffed it, held it up to the light. A look of sudden realization spread across his features, but with a glance at the cabbie he quickly made his face emotionless. The cabbie didn't notice; he was still talking, going on about being bored or something like that. Not that Sherlock was listening anymore.

Then both of them swallowed the pills.

The cabbie promptly gave a crow of triumph. "You guessed wrong! Ha, ha, you fool! You fell victim to one o' the classic blundas—the most famous o' which is "neva get involved in a land war in Asia"—but only slightly less well-known is this: "neva go against a cabbie when death is on the loine"! A-hahahahahaha!"

Sherlock stared at the cabbie as the man continued to cackle, frowning deeply and wondering if he had accidentally deleted all memory of these "classic blunders" from his hard drive.

"A-hahahahahahaha! A-haha—"

A bang startled the detective out of his musings as a bullet ripped itself through the cabbie's chest, as well as the wall behind him. Sherlock spun towards the window with a snap of his coat. The only evidence of the killing shot was the hole in the window-pane, and a lightly swinging door in the building opposite.

(Time Lapse)

Sherlock approached John, who was standing behind the police tape, trying his best to look entirely innocent. The detective, of course, saw instantly through this façade.

"Good shot." Sherlock said quietly, giving his friend a knowing smile.

John tried futilely to hold back a grin. "I'm just glad I got there on time."

"Well, technically you didn't…"

John cocked his head thoughtfully. "Yes, I was wondering about that. To think, all that time it was your pill that was poisoned—"

"Sherlock!" Inspector Lestrade came jogging up beside him. "Sherlock, I have to talk to you."

Sherlock resigned himself to his fate with a huff. "Alright, what is it?"

"You both ate the pills before the cabbie was shot, yeah? And yet he only died of a gun wound, not poison, and you're still very much alive. I need to know what happened, Sherlock! Who took the lethal pill?"

"I did."

John and Lestrade both stared at him incredulously. "Then how—"

Sherlock spoke very quickly with animated gesticulations as he always did when explaining his deductions. "When he first held the gun to me I noticed a white powder stain on his sleeve, which had to have been caused when making the pills. It had been wiped away but not completely; some of it had been pressed into the fabric. I recognized the stain as one of five compounds which I myself have often used, all of which are entirely deadly…to most people. I could see that they had fallen in crystal form, the pattern of the stain made that obvious. That immediately eliminated two of the five compounds. It was only when the cabbie said that he had criminal connections that I was able to obviate another. One of the three substances is quite easy to obtain; I have to use criminal connections of my own in order to get the others…oh, don't look at me like that, Lestrade. I then chose one of the pills, and holding it up to the light I noticed that it had a slight sheen to it, similar to sugar. That, of course, left only one of the compounds as the possible composition of the pill. I knew immediately that I had chosen the bad pill but I was extremely lucky in this case. The poison was one that I had spent the last few years building up an immunity to."

John and Lestrade gaped at him with identical thunderstruck expressions. "Fantastic!" They exclaimed simultaneously.

"You really think so?" Said Sherlock with a smirk.

"Think so…?" John cried. "Why it's unbelievable…absolutely…" He trailed off, shaking his head in astonishment.

Lestrade stood frozen, stunned, his mouth working like a fish as he tried to find words to express the depth of his amazement. No such vocabulary could be found.

"I do believe the man's in shock." Sherlock deduced. "A blanket, can we get a blanket?" He called to the paramedics and gave Lestrade an encouraging shove in their direction.

"I expect your pride is somewhat hurt." John said as they strode away from the crime scene. "You did lose, after all."

"On the contrary." Sherlock retorted in clipped tones. "I won."

"But technically you lost." John explained. "You chose the bad pill. It was luck entirely that the cabbie used the right poison."

Sherlock cast John a baleful glare. "Yes, fine. I see your point." There was momentary silence as Sherlock stewed. Finally he smirked. "I suppose my pride is hurt, a little. But at least I know that I'll always have you to make up for my shortcomings."

"What? By shooting anyone who outsmarts you?"

"Exactly."

I guess that's bad luck for Irene Adler, then...

Forgive me if Sherlock's explanation is a bit off; I know just about as much about chemistry as Sir Arthur Conan Doyle knows about horse racing, haha.