From the first time Sherlock tilted his head to the right, it called to John. It whispered promises, taunted him, tempted him and if his cock didn't give a slight twitch every time it was bared, John knew he had to be seriously ill. And that was only once, when he'd had food poisoning, and even then the words "lips, neck, lips neck" kept repeating in his mind.
John had quickly realised Sherlock's neck was on the list of top five things he loved the most about his flatmate. It was easier when cooler weather came. Sherlock's coat collar would at least be turned up if his scarf wasn't present. When temperatures only called for Sherlock's basic suit, were problematic. Ignoring that pale neck was as likely as Sherlock ignoring four serial suicides.
Despite what others may think, John notices things. He knows Sherlock has been glancing his way when the detective believes John is unaware. One summer afternoon Sherlock sat dozing in his chair, head tipped back, and John lost the will to fight. He ran his fingers down the slender neck, ghosting over the Adam's apple. Leaning forward, John tucked his nose and mouth against the side and inhaled as arms wrapped around him.
"Finally," Sherlock murmured.
John then realised he'd fallen neatly into Sherlock's trap, "You sneaky bastard."