Haven't had a high school reunion yet, but here's a fun one from my Mom's third reunion.
She went with my dad back to her hometown for the reunion. My dad grew up in a different place, so he didn't know anybody there. Bored out of his mind, he decided to have some fun and found a way to discreetly ask someone who the biggest juvenile deliquent, troublemaker was in their graduating class.
Let's call him... Albert Davis.
So, my dad went to the nametag table and found Albert Davis's nametag. He put it on and went around saying hi to everyone just to watch their reactions, because most of them assumed that Albert Davis was in prison.
My mom did not think it was funny.