Senior prank
A senior prank, also known as muck-up day in Australia and the United Kingdom, is a type of organized prank pulled by the senior class of a school, college, or university to cause chaos throughout the institution. The pranks are usually carried out at the end of the senior school year as a going away mark on the school, and in some cases have become something of a tradition. The pranks are often planned out very well before they are actually done in order to work out details such as not being caught or blamed for the  disruption they cause. Often these are harmless and more often hilarious pranks, but sometimes the pranks can be taken too far, causing serious problems such as damage to school property and resulting in arrests and large fines. United States. The practice has been banned within some schools in the United States, and replaced with formal leaving activities to ensure students do not commit crimes or vandalise school or other property. United Kingdom. In the United Kingdom, "muck-up days" are common in independent schools and state schools, and members of staff (particularly grounds staff and porters) often unofficially assist the  perpetrators. Examples of such traditions include stealing the school's clocks as makeshift trophies or removing styluses for interactive whiteboards. Australia. In Australia, muck-up days are a common practice in many schools, although their nature has evolved over the years such that activities are usually pre-approved by staff (e.g., a year coordinator) and may not harm staff, students or property. Notable pranks have been dyeing the swimming pool purple and bringing pigs to school. Common pranks. Common senior pranks include but are not limited to: adopting unusual or fancy dress, using water pistols, stink bombs, water bombs or  shaving cream on each other or on teachers, issuing fake announcements over the public address system, starting barbecues in unusual places, imposing parking levies on the staff car park, issuing staff with detentions or uniform infringements, putting small polystyrene balls in the air conditioning, thus making it 'snow' in the building, chalk graffiti, filling elevators with hay or spreading bird seed in the staff parking lot to attract birds that then deconstruct the cars, setting up tents and making it appear that the seniors had camped overnight on school grounds, or having a party in a faculty/underclassmen parking lot  to confuse the parking situation. At some schools that ordinarily have strict uniform policies, teachers turn up in full school uniform on the day, and the students in free dress. Some schools announce a day off for the rest of the school, while others conduct an assembly to formally farewell the final-year students during the day's events. More extreme examples. Incidents such as graffiti, vandalism or harming other students are dealt with in a number of ways, as the students despite finishing school have not yet graduated and, in the case of students enrolled in academic subjects, have  yet to sit their exams. In extreme cases, or those involving non-students who turn up on the day, the police may be called. At Scotch College in Perth, the Year 12 boys' valedictory dinner was cancelled by the school after some students vandalised and ran partially naked through two nearby girls' schools.