Sherlock was grinning. This was concerning at the best of times, but now, in the enclosed flat, it was downright alarming. John stepped into the living room with trepidation, unsure of what precisely his partner was up to but certain that he wanted no part in it. The detective continued to smirk, but not at John, at some point above him.
John looked up and immediately began to laugh. "Really, Sherlock? Really?" He sat down on the edge of the chair. Honestly, it shouldn't have struck him as this funny, but there he was, his sides starting to ache he was laughing so hard. Sherlock gave him an aggravated look.
"John, it's not that funny," he insisted, but John only shook his head falling further into his seat in amusement. Sherlock scowled, pulling his knees up to his chest. John, with no small effort, got himself under control and moved to sit next to Sherlock.
He pressed a small kiss to the detective's cheek. "Don't be cross, I'm only teasing," John murmured. "It just- well, you have to admit, it's a little funny." John grinned when Sherlock pulled back a bit in annoyance. "Oh, come on, the great Sherlock Holmes, laying in wait to ambush his flatmate under the mistletoe? What would the tabloids say?" Sherlock started to get up, but John tugged him back down, knocking the detective off-balance so that he fell into John's lap.
He drew him down for a chaste kiss.
"All right," Sherlock mused a moment later. "Perhaps it's a little funny." John smirked, leaning forward to kiss along Sherlock's jaw.
"I'm just annoyed you didn't think of it sooner," John replied, whispering in Sherlock's ear.
"We'll just have to make up for lost time then," Sherlock replied easily.