Sherlock had just solved an incredibly complicated murder (the details are unimportant as this is not a story about plot but it involved a well known member of the house of lords, a ballet slipper and a literal red herring) with such a flawless, stream of logic that the murderer (the dishwasher at the Red Herring fish and chips shop) was rendered speechless. Lestrade was on his way to arrest him.
"And the speck of dust on your shoe proves beyond doubt that you were in Manchester on Thursday where they have a unique kind of dust that only appear on Thursdays when the factories dump their toxic waste. How disappointingly simple."
Sherlock looked so brilliant and Sherlocky while he delivered this important bit of exposition, that John had to kiss him right then and there.
"Bloody poofters," muttered the murderer Britishly.
"That was remarkably bad timing, John," said Sherlock, his expression unreadable.
John's face turned red.
"Look, just forget it, ok?" he said and stormed off.
"Where are you going?" said Sherlock.
"I'm storming off," said John, glancing back over his shoulder.
Sherlock looked at John, then at the murderer and back and then he took off running in John's direction.
"You know, generally when people storm off, you're not supposed to follow them," said John.
"Mmm," said Sherlock.
"What happened to the murderer?" asked John. "Did you just leave him there?"
"Oh him," said Sherlock with a shrug. "I decided you were more important."
He kissed John with rather more enthusiasm than the last time.
John really didn't want to stop kissing Sherlock but he felt obliged to ask, "What if he runs away?"
"Then we'll have to catch him again," said Sherlock grinning. "Won't that be fun?"