The only mistake was recording the prank and showing it to other kids - other than that, I'd have no problem with what they did. It's teach the kids a lesson not to go through other people's stuff.
ShepherdsDog ShepherdsDog:
They were punked

a grade 8 grad party

. Getting through Grade 8 isn't a major accomplishment. Kids seem to expect rewards for the most trivial shit nowadays.
No doubt - my niece's school held a 'graduation ceremony' for the kindergarten class, complete with robes and 'diplomas'. Hell, I didn't even go to my junior high school grad at the end of grade 9.