sabotage
as a whole, the year 12 class i graduated with had a pretty decent relationship with the principal, and as such we had made an "agreement" as to what would be tolerated on muck-up day and what wouldnt

muck-up day went off without a hitch, the morning being full of relatively harmless fun, with teachers feeling sorry to see us go and commenting all day on our high maturity levels

cue to a week later when yr 12 exams are getting underway and a very large, very well drawn penis is dicovered scrawled across the middle of the school oval, drawn in dead grass. round-up had been used on muck-up night to give students time to make up alibis before the round-up had finished its work (round up being weedkiller of course)

cue to the schools annual "melbourne cup day" (school is in victoria) festivities, where all photos taken of the events had to be photoshopped to remove the massive cock from the background ;)

a group of year 7 girls had to be told by the teachers that, for them, the front oval was out-of-bounds as the teachers couldnt stand to see the girls naively playing around, and sitting on, the year 12 handiwork which the girls clearly didnt recognise
(dawa, Sun 8 May 2005, 9:03, Reply)