The Yarders make a bet about when John and Sherlock will get together, not knowing that they already are, in fact, together.

…

"No, no, no. You're all wrong. Three months, max."

"Seriously! Are you paying attention? John says he's not –"

"He can say anything he likes, but we don't have to believe him."

Dimmock smirks. "Well, I think he'd know."

"Maybe he's just in denial."

Anderson nods, taking another sip of his too-hot coffee. "Definitely denial."

"I mean, have you seen how they look at each other?"

"You can practically smell the gay."

"Exactly." Sally crosses her arms, looking smugly proud of herself.

Lestrade rallies the group again. "So, let's review." He clears his throat and gestures at the sheet of paper they've written their predictions on. "Sally says three months max, Anderson says two weeks, I say a month, and Dimmock says never."

Sally snaps, "Why do you have to be suck a fucking killjoy, Dimmock?"

"Why are you getting so defensive? You hate 'the freak'!"

Sally nods, conceding that minor detail. "It's not a matter of liking someone or not. It's a matter of observing and deducing..." Sally catches herself echoing 'the freak' just in time. "I mean…"

Lestrade's smirk shuts Sally up. "How confident are you about your prediction?"

Sally nods. She's not about to back down now. She thinks her prediction is optimistic at best. "Three months, definitely."

"Never. They're never getting together. You can't convince me." Dimmock shakes his head, and Anderson just shrugs.

Lestrade nods, breaking out laughing.

"What's so funny?"

Lestrade can't talk he's laughing so hard, so he just points to the window behind Sally.

Sally turns, and to her great surprise, sees John and Sherlock strolling through the Yard's office holding hands.

Dimmock's mouth falls open in shock. "Oh my god, they're already together."

The shock is multiplied 20,000 times when John and Sherlock stride confidently up to the window, look right into Dimmock's eyes, and proceed to kiss while John flips Dimmock off.

Lestrade just laughs.

Based on the LWS Trope Bingo Card 4 prompt 'Making a Bet'.