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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My elementary school bathrooms were always flooded with around an inch of water and other liquids.......... Oh, and I once threw up on my 3rd grade teacher :D