It takes more than two actors natural chemistry to create this level of fuckary. Two actors can spark off one another till the cows come home but unless their surroundings, what they're doing and saying hints at something more, it pretty much goes unnoticed or is put in the friend zone. For example let's look at John and Sherlock's date at Angelo's. What makes that scene so date-like is well, everything. 1: Setting. They chose to use a small intimate restaurant, with low lighting. They could have had them in a pub or hell even a takeaway like McDonalds or the Chicken Shop. A kabab house even. Those kinds of places are everywhere in London, and give off a much less intimate vibe. A pub would have very much placed they're relationship in the friend zone. 2: Lighting. Pink. Now I know that pink was the theme of the episode, but was having Sherlock bathed in pink really necessary? They could have put pink in that scene in any number of way but chose that. Plus, again the dim lighting of a restaurant sets a different vibe than say a dim lighting of a pub. Its all about intimacy. 3: Why the candle? Most restaurants I've been to, specially small intimate one like Angelo's, will already have a lit candle on the table. They did that so as to draw attention to the fact that this is a romantic intimate date-like scenario. If the candle had already been on the table, like normal, the audience wouldn't have noticed it. It would have been brushed off and Angelo would have had no need to mention it being a date, which would mean John couldn't have said its not. Which leads to 4: What is said. With Angelo's casual insinuation that its a date and John & Sherlock's conversation about their love lives and sexuality, its all put together to point out that there's an underlying sexual tension. While its logical that John would be quizzing his new flat mate on his love life, in a casual getting to know you way, his reaction to Sherlock's answers are anything but casual. And that Sherlock assumes he's being chatted up after being seemingly oblivious to Molly's attempts earlier is telling. Its the writers telling the audience that Sherlock does know when MEN are interested. Now this could maybe have been pulled of as a joke, if not for all the above reasons. If this conversation had happened in a pub, it may not have been so easily recognized as date-like and would have like felt like two blokes getting to know one another. 5: Directing: While yes, John's lip lick and gooy eyes were probably acting decisions on Martin's part, its highly unlikely the director would have allowed it if that wasn't the tone they were going for. He would have done retakes. Unless of course Martin pulled a Shatner and mess up every other take so they'd have to use that one, which seems unlikely, because they're nothing to be gained from it. The intimate close ups of John and Sherlock looking at one another, again directing decisions. There's also the music and editing to take into consideration. All of which add to the mood of the scene. So the idea that Johnlock exists purely because Martin and Ben had just too much screen chemistry to be contained by this show and that it's all on them is laughable. They're just two little cogs in a much larger machine.
