Abruptly, Seamus stopped coughing and grinned up at Dean. "A man could die while you mucked around getting water," the brat said, taking the water anyway and drinking it anyway. Making fake choking noises wasn't all that pleasant for his throat, but it had been worth it to see the look on Dean's face.
He fully expected a thump on his head for it, so he quickly swallowed the mouthful in his mouth and preemptively flinched away.
Okay, so it wasn't so nice to pretend he was choking to death...but the face Dean had been making had been hilarious. Seamus was pretty immature when it came to what kind of humour he usually indulged in. Scaring the living wits out his best friend? Hilarious.