well these are nothing compared to some of these, but there are a couple that come to mind, each disturbing in their own little way.
at my high school. There was graffitti under the table, and it included such gems as "I fucking hate Kikesville" (the schools name was pikesville) and "(swastika) was here". It was the first time I'd ever really come face to face with legit anti-semitism
At a friends house one time, we'd been playing around on the couch cushions and for whatever reason my friends parents came down and started what I can only describe as verbally abusing him. nothing says a nice afternoon with friends like hiding awkwardly in the corner while said friend is berated for no reason what so ever.
On a trip to Israel, while I was waiting in line, I watched a man collapse of heat exhaustion, a rather blunt reminder to take those warnings about sunscreen and water seriously.
Two years later, on a different israel trip, after a three-day long hike, while we were taking part in closing ceremonies beneath some eucalyptus trees, there was an enormous crack heard above us, and while most of us managed to get out of the way just in time, our guide, who I was standing pretty close to previously was laying face down underneath a tree branch the size of a tree.
and lastly there was a time when I saw my grandmother, who was in the advanced stages of Alzheimers. She was listening to old music and her fingers were twitching on the arm-rests and here eyes closed tight, giving me the impression, even at the time, that she was engaged in some terrible struggle with the outside world. And when she opened her eyes, they seemed empty and void. she was a shadow of her former self to say the least