Sam tipped back his beer chaser, rocked backwards and hurriedly gripped the bar. "OK, time to go."
"Don't throw in the towel, yet, Sammy! It's your birthday!" Dean insisted, adding cajolingly "just one for the road."
Sam sighed. "Just one."
Grinning wickedly, Dean produced a glass of varicoloured liquids, umbrellas and plastic monkeys. "Chug, chug, chug," he recited quietly, lifting the straw to his brother's lips, growing ever louder as Sam's cheeks gradually hollowed and his eyes crossed.
Outside, watching Sam trip over the kerb and face-plant on the tarmac, Dean wondered idly if that's where the expression came from.