Sherlock is approached to be a model during his time at uni, while he’s still using cocaine. While he’s initially scornful to the idea, he then finds out how much he’d be paid. That much easy money for walking around in some tight clothes?
He does it, and falls into the party lifestyle, spending his time getting high and never meeting Lestrade or becoming a consulting detective.
Add one John Watson, and what happens? Do they meet earlier and does John save Sherlock from himself? Or are they torn apart by John’s commitment to the military? Or maybe they meet where the series starts, somehow crossing paths even with their wildly different lives.
Johnlock preferred, but gen is fine.