Sebastian proposed to Jim, who exepted (possibly because he found the idea as hilirious as I do...). Problem is, neither of them has any friends, so Jim thinks it's totally reasonable to ask Sherlock to be the Best Man. Sebastian doesn't. John does neither. Sherlock, however, seems to understand Jims logic, as twisted as it might be.

Make it as deadpan and 'serious' as possible. I love my crack to be served dry.

(Okay, this one is too good not to share. Mycroft!Captcha asks: "What is for dinner?" :D )