one of my favorites:
In the 3rd grade we visited the post office for some reason. In the middle of the mailroom floor some kid decides it's time to puke. Some mail guy in a hurry with a big cart comes racing through it. He didn't realize what he just did until there were vomit tracked across the entire floor, with footprints of vomit clearly visible. That dude was as pissed as, well, a postal worker.
One of my least favorites was visiting the city sewage treatment plant where you walked on iron catwalks over what appeared to be hot tubs of shit. Impressively there was no vomiting this day.
feel free to add.