Venting frustrations

I know I am just complaining and it is all my fault at the end of the day, but I really want to chid someone (but ultimately the blame is mine really) for what just happened.

I was supposed to be an invigilator today and what essentially happened was I slacked in my duties. What happened was each colleague is supposed to be in charge of their particular wards and I would just be an overall in charge. Subsequently, I was working with colleagues from my own department, so to me I felt there was a mutual trust between me and my colleagues. In the end, there were some (minor) hiccups, thanks to my oversight. As the invigilator I had to run back to the rooms and remind the colleague. This not happened once, but twice.