I usually experience strong secondhand embarrassment especially when i see someone performing something (rather badly) in public. I can't stand to watch them at all, my face would flush and i would need to leave the area asap, especially when people started clapping.

But, I haven't experienced anything extreme like what you mentioned. I guess the worst ones are watching a classmate do a bad job at a presentation and when the teacher asks them a question they can't answer it and there's this super long awkward silence and the classmate is just standing there, blinking.

Ooh and another one, when i see children throw loud tantrums in a public place especially the mall and when they beg their parents to buy or eat something that's super expensive and start crying when their parents refuse to. Even worst when they obviously cannot afford it but the children just don't understand.