In 5th grade inside one of the boy's bathrooms, there was a giant turd in the middle of the floor nowhere near the toilets. It smelled pretty bad in there too, probably because of that turd. There was also poop smeared all over one of the stalls.
Other than that, there hasn't been anything really disgusting ever since.
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Here's a funny one. Our student body president put up an advertisement for the snack shop that said "if your sofa king hungry, come visit the aces snack shop" it was up for two weeks before anyone figured it out and they they got suspended with community service.