This is a fill (no, really) for this prompt:
Sherlock lets slip in attendance of Scotland Yard that John likes knitting, which causes embarassment. When everybody departs, Lestrade stops John.
"So you knit, then?" - "Yes, yes, I know, not a typical past time for an ex-uniformed man." - "Yeah, yeah.... I just wanted to ask..." *gets out a magazine* "I quite like this cable pattern here, but the instructions are all in some sort of code. I only really do basic patterns...."
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John was sure that his cheeks would explode from the amount of blood that suddenly rushed to them, making his face red os a USSR flag. The sudden silence taht followed Sherlock's comment was making everything even worse, because, well, it's hard to say in very masculine and badass way "oh, shut it! Got a problem wth THAT" when no one is saying anything. John almost wished that there was a sudden and quick zombie attack on the station, so he could immidately replace the image of 'knitting, grandma - like, cute Johnny' with 'OMG, look at his KARATE CHOP'.
And Sherlock's utter suprise was not helping. At all.
'Did I say something... wrong?' ask he finally, not bothering to lower his voice, with bafflement apparent. Before John could formulate something more sophisticated than 'I'MA KILL U FOOL', Sally provided better and more accurate answer.
She started histerically laughing, doubling over in vain attepmpts to conain it (or ratcher, to pull some air into her lungs).
'Can you imagine' she gasped between fits of laughter 'Dr Watson, with kneeting needles...'
'...in front of the fireplace, covered by the blanket...' supplied Anderson, smiling maniacally.
'...with ound glasses and tight bun on his head?' she finished, supporting herself on a table. There was a bit of silence, then, when John tried desperately to think of some witty remark (keeping one eye on the window, where are those ninjas when you need them?) and the rest tried to process the mental picture.
And then, there was a roar of laughter. So loud and so histerical that people from other offices snuck in just to see what is the party they don't know about.
Sherlock shrugged, in 'humanity is stupid, but I won't take toys from those mental children' way. John tried to maintain his composture.
"Ha, ha, ha, you had your laughs. Now I'm leaving, and let me tell you, I will never move a finger if an angry alien tries to kill any of you!" he snarled, causing another wave of laughter and something what sounded suspiciously like 'omg, killing aliens with knitting needles!' from Anderson, who just fell down from a chair.
John just left. Waking as fast, as his damned leg allowed, head held high, he tried to be an adult who can laugh at himself... and was failing miserably.
'John, JOHN!' he heard a shout from behind. Lestrade, still flushed and sligthtly breathless, jogged up to him. 'John, about your knitting'
'Want to look like a panda?' challenged John, not caring now if he was about to assalut DI on the police station. Lestrade had a decency to look ashamed.
'Weeeell, I'm sorry, I really am! And I'm going to talk with Sally, but you must admit, imagining you as an old grandma...' one look at John's expression was enough to radically change Lestrade's sense of humor. 'No, I suppose not. But, John...'
Lestrade look around, as if in search of spies or hidden cameras in this empty corridor. He took out a front of the ugliest pink sweater with orange pompons.
'John, I tried to make a flower here, and here, with cable knitting but it just doesn't WORK!' he whined. 'Could you tell me what would you...'
John did not hesitate. He took out from his pocket a knitting magazine (which started the whole situation) opened it on the proper page, and motioned Lestrade to come closer to look.
He also didn't hestitate to smack Lestarade in the face with this damn paper.