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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In the third grade, one of my classmates had to throw up. She got up and ran to the garbage can, but another kid was in front of it. He didn't move fast enough, and the girl puked all over him. Then, the nasty old smoker janitor had to come in and clean it up, which was really awkward.