"If your imbecilic team hadn't messed up the evidence, I wouldn't have hadto break into the Yard's evidence lockers in the first place," Sherlock said defensively. "Really, Gary, you shouldn't get so worked up over trivialities."
"Trivialities?" the DI exploded. "Alright- alright, Mr. Genius Detective. You could have maybe asked me- no, of course you wouldn't, you don't even know my bloody name!"
At that, the Consulting Detective looked genuinely insulted. "Of course I do! I just used it, didn't I?"
"Then let's hear it. What's my given name?" the DI challenged.
Sherlock frowned slightly, his forehead scrunching in thought. "I'm not an idiot, Giles."
"That's exactly what I mean!" Lestrade roared, slapping his temple in exasperation. "You know what, Mr. Consulting Detective, let's pretend this is a case. Why don't you just deduce my name?"
"Deduce?"
"Exactly. If this was for a case, you would know my name in a flash, instead of taking years to learn it. So, Sherlock Holmes, would you please take my case? Or is it beyond your abilities?" the DI added snidely.
"Alright. I've got this. Your Christian name definitely begins with a "G", as the "G" in your signature is quite distinctive, and is the only legible letter in your signature."
"Great, you've analyzed my signature, and still can't remember my bloody name," Lestrade muttered.
"Now, the question is whether the "G" is hard or soft. I would say 'George' or 'Geoffrey' would be a nice, suitably boring name for you- but if it were soft, it would have alliterated with 'John,' and I would definitely have noticed that.
"Your name is most definitely a common, dull one, or I wouldn't have such a hard time remembering it," Sherlock continued, tapping his chin thoughtfully, completely oblivious to the DI's growing frustration. "That rules out names like Garrett or Griffith.
"I would say it's more than one syllable, according to the length of your signature. So, not Giles or Grant, then. Your parents liberal leanings and atheistic orientation would rule out Biblical names, so no Gabriel or Gideon."
"I don't know whether I should be impressed by your deductions, or appalled by it, considering how many times you've heard my name, and still haven't ever gotten other correct, even by mistake," Lestrade said sarcastically.
"Your name isn't one that's commonly used as a last name, or people would have confused it. For example, if you introduced yourselves to people by your first name, they might have called you 'Detective Graham,' or 'Mr. Grayson.' I've only heard those titles being used with your last name.
"Considering the above, I would narrow down the options to one of the following: Gavin, Gilbert, or Grover. Which one is it?"
Lestrade gritted his teeth, and then took a deep breath, blowing it out in a huff. "How about Gregory?"
"No, can't be. You call yourself that when you're undercover, don't you?"
Sherlock eyed the DI's bulging eyes and clenched fist with apprehension. "You know what, I don't know why I bother," Lestrade hissed, and stomped away dramatically.
Sherlock smiled to himself. The man had it coming. Greg could be so annoying sometimes.