Remus and Peter pulling a prank on James and Sirius:
"Did you bring them?" Peter asked, eyes shining bright with suppressed glee.
"Yes" he whispered, patting his pocket with triumph "but wipe that smirk off your face, or they're going to get suspicious."
The two boys waited impatiently for their friends to arrive on the platform, leaving Remus and Peter to continuously jitter with anticipation. Remus still couldn't believe it had taken them two years to think of this.
Finally the two black haired youth's made their appearance, and the other two thirteen year old's burst in front of them with unfounded glee as they practically forced their friends into a compartment they had already cut off for themselves.
"What's got you two in such a rush?" Sirius asked, unable to keep a smile off his own face.
"We brought you something" Remus grinned.
"Me and Remus have been sending each other owl's all summer about some of the things you lot have never experienced in the muggle world" Peter explained before the two could ask "and so we snuck a little something on the train for you guys to try."
Intrigued at once, James and Sirius suspected nothing as they were each handed a can.
"It's called Pop" Remus explained, letting a little of his exuberance start to creep through "it's like nothing you've had before."
The two boys made to open the tab's, but Peter quickly said, as if just suddenly remembering "Wait, we didn't tell you. First you've got to shake them up a bit, make sure the flavor hasn't settled at the bottom."
The poor unsuspecting Purebloods thought nothing of it as they shook up their can's very well, and didn't seem to notice there friends had backed all the way to the compartment door when they finally cracked open their drinks.
Twin brown fizzes shot out of the top, hitting their holders in the face, and didn't quite stop even as they were released to the ground. The carbonation got everywhere, shooting up to the ceiling, making sure to splash across the window's and dowsing their trunks as well.
By the time James had taken off his glasses and found something dry to clean them off on, he replaced them to find Remus and Peter, not having been saved so dripping as much as them, on the sticky floor, laughing. Sirius and James exchanged a proud smile before joining in.