"This is your fault."
"It isn't! I swear, Merlin's honor, I had no idea he'd do this."
Lily looked at James. A lantern swung about drunkenly; James still rubbed at the sore spot where his head had met it. He seemed sincere, at least, but that was one of James's special talents: even more than transfiguration, he was skilled at affecting sincerity. Her heart gave a great thump. She'd watched him swerve his way through Hogwarts, avoiding more detentions than he'd served. How could she trust that he meant everything he seemed to want to do for her? She swiped her sweaty palms on her robes. It was the near the end of seventh year. They didn't have much more time.
"If I find out you have conspired with Sirius—"
"I haven't! You know him — he's a badly trained dog," James protested.
"If I find that out, it will take some convincing for me to let you kiss me again." Lily folded her arms across her chest. Her heart had ceased thumping and was now thrumming: fast, uneven, threatening to leave her chest entirely. This is it, she thought. This is the moment.
"I didn't — wait," his voice dropped. The lantern's light was more or less steady now. James's hazel eyes widened. Lily could see the impact of her words writ on his face, as though she'd hit him with a slow-acting hex. "Kiss you — again?"
"Yes, James," she said. To her horror, her voice broke. "I'm tired of the teasing from your little boy gang. Pranks or kisses. Choose one."
In the end, Lily near forgot that they'd been locked in that dusty old broom cupboard by an unknown third party (at their wedding, she learned it had been her own friend Marlene McKinnon). James made the right choice, then, with a desperation and intensity that made that cupboard seem a rather a fine place to be. After a kiss that made her toes curl in her shoes, he leaned his forehead against hers and sighed. Her questions of his sincerity were swiped away. Heart still thrumming, she cupped his jaw, thumb stroking him, she proved her own sincerity and pressed her lips to his.
No more pranks. Just kisses.