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The abbreviation of Muck Up Day; a tradition that occurs in many schools (mostly private) on the last day of lessons for year 12s. Pranks are pulled on the rest of the school, including kidnappings, stink bombs, cod liver oil on banisters, viagra in the water supply and releasing three sheep labelled 1, 2 & 4 onto the school grounds (the groundsmen look for sheep #3 which doesn't exist). Students also personalise their uniform (rip it up...). Water guns/bombs are also used and occaisonally students will hiijack the PA system. School shirts will often be signed with 'MUD (insert year)'.
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