I should have tried something like this before I retired...I'm sure I could have gotten the bailiff, clerk and court reporter to go along with it.
I was in a "Flash Mob", as they were later called, at school. There were about twenty of us. Everybody went into the University Library at precisely 2:17 p.m., wearing jeans and white tee shirts, and all asked for help with a paper on the Gilgamesh Legend. The librarians started by taking us seriously, then they just laughed and laughed. At 2:19 p.m., we all left.
I saw one of these on YouTube where a whole group of people stopped completely still for a few minutes. It was so strange!