John had to stop gritting his teeth. If he kept this up, he'd be due for an entire day in the dentist's chair to repair the damage.
Sherlock and Mycroft had been going at each other all week. Sherlock wouldn't leave this case alone, despite Mycroft's attempts to direct his attention elsewhere. Then Sherlock needed Mycroft's help in searching a restricted database but refused to agree to any kind of deal. The count of laptops sacrificed to Sherlock's stubbornness stood at three so far but was likely to climb.
Now it had all come together at this crime scene. Sherlock was pouting. Mycroft was seething (although he outwardly looked the same as always). Lestrade was working. John was staying out of everyone's way while keeping an eye on a particularly stroppy consulting detective.
Sherlock finally snapped, stalked over to Mycroft, standing by his dark car, and began hissing out insults under his breath. This was not the way to convince Mycroft to leave, of course, but Sherlock tended to loose sight of expediency when it came to needling his brother. Mycroft was giving back as good as he got, as no one knows the soft spots like family, and if he occupied Sherlock's attention, Sherlock couldn't investigate any further.
The basics of the scene had been covered, so Greg looked up and around. When he spotted the Holmes brothers arguing, he began moving in their direction. John drifted behind, ready to dampen any fireworks or treat any resulting wounds.
They all heard Sherlock grind out, "I just want you to leave!"
Mycroft's response was a frosty, "My responsibilities must take precedence over your whims, brother dear."
Greg stepped in. "Mycroft, we're about done here. It would be a help if I didn't have to worry about your presence."
Mycroft promptly gathered himself to leave. "Of course, Detective Inspector. I will contact you tomorrow for a status update." He entered his car, which drove away.
John didn't actually see Sherlock's mouth drop open, but it was a near thing. He whirled to turn on Greg. "Lestrade! No one makes Mycroft do anything! How... Why..."
Greg shrugged. "Maybe it's my sparkling personality. Or, dunno, asking nicely instead of needling. Now off you go as well."
John smiled, guiding his flatmate away. Sherlock was so gobsmacked all he could do was say, "But John!"
"All right, Sherlock. Time for dinner." John patted his arm and kept him walking in the right direction.
"Why would Mycroft listen to him when he ignores me?" Sherlock seemed honestly confused.
John discarded his first few answers and went with the simple response. "That's what one does for one's boyfriend."