I had just finished one of my GCSE exams (2012), and they were letting rows of people out in "half rows" (from the back half of the line, then the front half) as in half of the row went, whilst half stayed til the half-line of people had gone.
I was one person below the half line, but thought (as I wasn't concentrating) that the whole line had been let go.
So I stood up, realising that the person behind me (with no one behind her) had not stood up, but then it was too late.
I couldn't sit back down and face humiliation, so I kept walking for my bag, at the back of the hall.
EVERYONE was looking, and I just grabbed my bag and left. It was SO EMBARRASSING.