'I don't know why you think that was acceptable?' John says incredulously, standing in front of Sherlock, gazing up at him, a look of disappointment transforming his stare from affectionate to hard.
'Oh, come on,' Sherlock says, tapping his foot against the ground, 'it was only a joke. You know what Molly's like. She'll take offence at anything.'
'You told her she looked fat. In the dress that she bought specially for this little party, which you invited her to, Sherlock,' John says ruefully. 'You know what you did. You know exactly what you did. And now we are minus one, and now she is crying on the bus all the way home. You just can't stop yourself, can you?'
He sounds almost weary.
'Get on your knees, please.'
Sherlock starts. What?
'Um. I don't understand?'
John could laugh. But he just can't be bothered.
'Knees, Sherlock. Now.'
It's the voice change that does it. It's not that it is any less soft than usual, but there's something, something hard underpinning it, something that makes Sherlock's knees wobble, and that sends him straight onto them, without another word.
John walks away, leaving Sherlock to shiver on his knees, knowing he's about to get punished in some way or another. He doesn't like getting punished. Oh god. He really didn't think he'd said anything rude. He was just being honest, after all. It's not that Molly is fat, after all. It just perhaps was a little tight around her midriff. It's-
His reverie is interrupted by John's return. John steps over to him, laying a towel down in front of him, a small bowl to one side. He kneels in front of Sherlock, holding his chin firmly, fingers crunching around Sherlock's jaw, grip hard and uncompromising.
'Open up,' he says, pulling on Sherlock's jaw, and Sherlock does as he is told, feeling dizzy spurts of adrenalin jump through his body, practically burning his skin. What is going on? This is not. This is new.
And then the sickening taste of something disgusting. He closes his eyes momentarily, not stirring from his frozen position, knowing he will receive a spanking if he moves when he's been told to stay.
Something thick and vile rubs against his tongue, coating it repeatedly, before John presses his jaw closed, and he is choking on the thick rectangle, gurgling around it, nausea rising in his throat.
'You need to learn that you can't speak to people like that, especially not Molly,' John says sorrowfully, stroking his thumb over Sherlock's cheek, watching him try so very hard not to gag. 'Suck on it, please, Sherlock.'
Sherlock does as he is told, wincing at the sickly taste. He chose the soap, but that doesn't mean he ever wanted to taste it in his mouth. John produces a bottle of liquid soap, normally kept by the sink in the kitchen, and presses the nozzle against Sherlock's lips, squirting a tiny bit into the corners of his mouth. It smells like milk and honey. It doesn't taste like that.
'Don't swallow,' John says, opening Sherlock's mouth, clasping the soap with his fingers, rubbing it over Sherlock's tongue. 'Stay still, there's a good boy.'
Sherlock wouldn't dream of doing anything else. He finds himself rapidly slipping, feeling very sorry, feeling very. Very. John's. Please. Please, he is sorry.
John takes the soap from his mouth, causing him to half-retch, rubbing it easily over Sherlock's favourite toothbrush, before he begins a horrible parody of the nightly ritual, washing it over his teeth, rubbing it into his molars.
'Are you sorry for what you said?' John says, squeezing Sherlock's shoulder with his free hand, noticing how hazy Sherlock's vision has become. He knows where he is right now.
Sherlock doesn't dare nod. John knows he is, now.
Five minutes later, he removes all implements from Sherlock's mouth, and allows him to gag repeatedly into the bowl, stroking his hair as he does so, telling him how good he is, before he washes his mouth clean of every flake and squeeze, pulling the contrite detective to him when he is done.
Later, he takes Sherlock to Molly's, where he apologises for being so rude. Molly looks stunned at the apology – and the flowers Sherlock haltingly suggested, still halfway in subspace when he does so – but John is thrilled at the response. He'll have to wash Sherlock's mouth out with soap more, if it ends like this.
He lets Sherlock suck him off when they get home, after Molly has plied them with hot chocolate and told them all about her Christmas plans, while Sherlock pays rapt attention and makes her feel extra special. Sherlock really can be such a good boy. When he wants to be.