Sherlock and John Accidentally Negotiate a Scene

John's off-handed threat to tie Sherlock up spirals a bit out of control. Or maybe neither of them were all that in-control to start with. Either way, it ends up with Sherlock tied to a chair, John being delightfully creative, and Sherlock doing his darndest (and failing miserably) to stay aloof and unaffected. Which is hard when you have a lapful of very warm, VERY horny flatmate.