A/N: The sin is gluttony, and the prompt is "favorite".

"Another treacle tart!" Dudley called loudly, sticking a pudgy arm up in the air.

"Haven't you had enough?" Harry asked. "That'll be your fourth, and you don't even like them."

"But you do!" Dudley sneered. "And all you can do is watch me eat, Potter. Isn't that right, Dad?"

Dudley grinned in delight as a waiter set down another plate of dessert in front of him.

"That's right," Vernon said, nodding.

"Dudders gets whatever he wants," Petunia added. "He's our favorite boy."

The Dursleys all turned to smile mockingly at Harry, who shrugged.

"He's going to be sick, you know," Harry told them.

Dudley's mouth was too full for him to respond, but his mother wouldn't stand for her son being insulted, especially by Harry.

"No manners at all," Petunia remarked, sniffing haughtily.

"That's what happens to boys with no parents," Dudley scoffed.

Harry said nothing, instead silently becoming angrier with every mouthful that Dudley gulped down. Eventually, his patience paid off, and his cousin's chewing slowed.

"Mum," Dudley groaned. "I don't feel well."

"What did you do to Dudley?!" Petunia exclaimed, as she started to rub Dudley's back.

"I didn't do anything!" Harry protested. "You've been watching me this whole time."

Petunia shook her head and looked to her husband as she tried to comfort Dudley, who was looking queasier by the second.

"I will not have these shenanigans while you are under my roof!" Vernon threatened. "Boy, you and your—"

Before Vernon could finish his rant, Dudley vomited the contents of his stomach onto the table. Vernon and Petunia rushed to make sure their son was okay, but all Harry could do was grin.

"I don't know what happened," Dudley whimpered. "I was eating and then I suddenly felt all weird!"

Petunia and Vernon immediately came up with multiple explanations, each more ridiculous than the last and each, of course, involving Harry. However, the nine-year-old boy in question wasn't listening to them. Harry was only thinking about one thing.

After all, he was sure that there was only one thing that could've made Dudley sick so suddenly—magic.