Random kissing shouldn't be a seasonal thing
Chapter 1: Set the stage
'What's this?' Stiles asked as a triumphant Lydia pressed a bunch of sprigs with a red ribbon tied around them into his hand.
'Mistletoe. What do you think? Help me put it up?' she proposed.
'I think that it's November,' Stiles reminded her. She ignored that. She was, in fact, already carrying a chair to the door.
'Christmas is a long way off,' he added. Lydia took exception.
'Showing affection isn't a seasonal thing. Or it shouldn't be, anyway. Spreading joy should be encouraged,' she argued. More like spreading mono, Stiles thought.
'Derek will hate this,' he pointed out instead.
'Does that mean you won't help me?' Lydia inquired. Stiles pictured Derek's reaction and grinned.
'Oh, I'll help you,' he replied. When Derek returned to the apartment with groceries, he found the two of them sitting on his couch, gazing at something over his head. Glancing up, Derek noticed the plant secured above the door.
'What's this doing here?' he interrogated. The 'in my apartment, where joy isn't allowed' was implied, but unmistakable. Stiles let Lydia do the talking.
'It's mistletoe,' she announced, not really answering Derek's question. She sounded cheerful. She also sounded as if she would fight him tooth and nail to keep the mistletoe up there. Derek sized her up and, apparently, decided it would be better to leave it. For now, at least. He'll probably tear it down and ritually burn it once we're gone, Stiles realised.
'It's November,' Derek grumbled, dumping the grocery bag on the kitchen counter before heading out again.
'Random kissing shouldn't be a seasonal thing, Derek!' Stiles boldly called out after him. Derek gave no sign of having heard.