Here's mine:
Due to my recent obsession over apples (getting people to add apple tags, having a sidebar full of apples etc.), I've been thinking about an event all about apples. The forum currency is measured in apples. The collectibles are applesauce, apple juice, candied apple, fried apples, apple pie, and apple cider. There are two contests, where one is a drawing contest (which has to be fall-themed or apple baking themed) and the other is a fall decorating contest (where you decorate one piece of furniture or a whole room with fall decorations). There can also be a lineart event (like the Bucket of Paint one) and hidden code puzzle (where you discover codes for apple redemption). The apple cider can be a contest award while the apple pie can be purchased if you found every apple (like the golden egg).