Geez, we were tame in comparison to these.
Apart from previous years, who were known to close off the teachers carpark and either park their own cars there or charge the teachers to park our school didn't do too much that was bad or over the top.
For my muck up day, we had two spray painted banners, one with a play on works for the school name that was hung out the front of the main office, and one with our grades motto (we came, we whinged, we annoyed) in latin (well internet translation, so probably incorrect) on the hall.
We also had the typical for sale signs on the school (tradition for most schools).
But our big thing was that we showed up early, before most people arrived, and removed all the chairs from the maths, english, history and humanities blocks (all were in one building) and turned over all the tables in those rooms.
Simple yet quite effective, until the principal, and her deputies told us very sternly (while trying not to laugh) to return all the chairs.
However the best one was the year before where there was a spate of gnomings in the weeks before the day.
When everyone showed up on the day, the school was full of garden gnomes. They were on buildings, duck taped to doors and just about every other place you could think. You could barely move a metre without seeing one.