Too many to name.
Once I was waving the Philippine flag in a stage play, and it got tangled up in the pole.
Another was when I was dating a classmate for the prom night, and got rejected in front of everyone.
Another was when there were group projects, and most of the time I would work solo since no one wanted me in the group. Yeah, I was an outcast/loner back in high school. And still am, at least most of the time.
Was there something you did that you regret in your life?