Bit of younger Sherlock/Lestrade here - feel free to skip if the idea of this pairing doesn't appeal to you.
Despite his better judgement, Greg trudges up the stairs, heading up to Sherlock's dingy single room in a filthy and suspicious building on Montague Street. Sherlock hasn't bothered him about a case in three days now, which means either he's found something more interesting to occupy his time, or he's in the throes of another binge. Neither option appeals much to Greg.
When he gets inside, the flat smells sour and bitter, sweat and unwashed linens. Sherlock is pacing manically in the tiny kitchen area. His hair is unwashed and his eyes are glassy, but most telling are the visible pinpricks of blood in his inner arm.
"You fucking idiot, Sherlock, what have you done? I can't leave you alone for more than a day. Look at you."
"I'm not a bloody child, I don't need you looking after me!" His eyes are wide and manic, his hands jittery as he waves them in the air.
"Clearly you do. Don't make me call your brother."
Hissing angrily, Sherlock grabs Greg's jacket and pulls him close, pressing their lips violently together. This isn't a kiss; it's an advancing front, a quest for dominance. Even in the sudden silence, their mouths remain at war.
Suddenly, Greg pulls back and runs down the stairs without a word, Sherlock trailing behind him, ranting and belligerent.