Dad graduated Ohio State. A large college by any measure, even back then. Dad decided not to participate in his college graduation. After all, he wouldn’t be able to make out the faces well enough to see who was there for him and no guests would be able to recognize him. He decided to pick up his degree in the office later.
Dad decided to make good use of the time by cleaning out his apartment. He left the television on for background noise. A local news station was covering the ceremony which is how he caught wind of what happened.
Apparently, a couple of his friends decided to make use of the vacant seat he had left. They filled an inflatable doll (an item I suspect is still readily found at institutions of higher learning today) with helium, and snuck it, fully inflated, past security. The pranksters then proceeded to dress it in a cap and gown. Then they finally wedged it firmly between them.
When the engineering students we asked to rise, one of them kept on rising!