One of my fave ways to pass time at work is sharing tales of mischief me / mates got up to at school, sure you've all got loads. A personal fave of mine is: Me and mate used to go into mobiles (temporary classroom blocks) at lunch time, first of all close all windows, then line up 4 tables so they went end to end from far wall to just behind door. Then we'd position another table just behind door, loop a tie around one of the legs (holding both ends in your hand), close the door (which opened inwards) with the tie underneath and use tie to pull the last table into place. Then unloop your tie and leg it. Result is door is jammed sceurely closed and cannot be opened cos of the 5 tables neatly lined up behind it. Only way in is for the caretaker to come and completely remove door surround, hinges / door. Did this loads of times and never got caught. Still cracks me up thinking about it.