John staring at Sherlock across the science classroom, mesmerized, but way too awkward to strike up a conversation.
Sherlock being perfectly aware of this and smirking whenever he feels John’s eyes on him.
The pair being forced to work together and a friendship developing, full of inside jokes and sarcastic comments and hours after school in the library trying to study but being too distracted by the other one to properly concentrate.
The quickening of both of their hearts when their hands brushed against each other.
Their first kiss, John asking Sherlock why he had gotten so angry when some girl in their class started flirting with him, and Sherlock blushing and refusing to answer, and then John grabbing his wrist and insisting that he answer and Sherlock spitting out "for God’s sake" and then grabbing him and kissing him passionately.