It had been nagging John since Sherlock had sarcastically snapped at Anderson. It shouldn't be – wasn't – a big deal. Really! It was just a word and more likely than not Sherlock found it on the internet and diagnosed himself. Probably thought it was the new black, or liked that it gave him an excuse to be awful and rude to everyone ever.
Even if he'd been diagnosed, a large percentage of people like Sherlock were diagnosed wrongly, and Sherlock was high-functioning anyway.
In fact, John should have seen it straight away. Sure, he wasn't specifically trained in the area, but they had covered personality disorders at med school and he was trained to at least recognise them.
So why was he having so much trouble accepting that Sherlock Holmes was a sociopath?
That question in mind, he decided to do his research. Sherlock was out for the day, he'd jumped down the stairs three at a time bellowing something about alphacetylmethadol and Furbies.
John logged on to his laptop and pulled up his new web browser that Sherlock had installed when he'd discovered John was using Internet Explorer. He wandered around Google typing in vague terms and using suggestions fed to him until he stumbled across a website about high-functioning sociopaths and how to recognise and respond to them.
John found a dot-point list of symptoms:
The Ability to Manipulate
Failure to Conform to Social Norms
Lack of Emotions
Lack of Responsibility
Absence of Personal Goals
As soon as John read 'Impulsiveness' he decided that Sherlock was most certainly not a sociopath. As he kept reading he found himself more and more confident in his conclusion, but without results it would be impossible to convince anyone.
So John decided that from now on, every time Sherlock did something that went against one of these dot-points, he'd write it down. He copy-pasted the list into a word document and titled it 'January Payslips'.