Yesterday, I took part in teaching a class. I prepared what I would speak about, dressed up for the occasion, and delivered my presentation. I received excellent feedback and felt I was behaving quite professionally.
After the lunch break, everybody was sitting and waiting for class to resume. I sat down and, right in front of everyone, I fell right through the chair, landing on my ass. We all laughed, my cheeks reddened (the ones on my face!) and we continued on.