Here are some ideas:

1. Googly Eyes Everywhere: Stick googly eyes on everything in the fridge, pantry, or around the house. It's super silly!
2. Silly Notes: Leave funny or confusing notes in random places. Like, "Please feed the houseplants cookies."
3. Colored Milk: Add a few drops of food coloring to the milk carton for a colorful surprise.
4. Fake Bugs: Put plastic bugs in unexpected places, like on a lampshade. Just make sure they're not too scary!
5. Frozen Cereal: Freeze a bowl of cereal overnight. It'll be a funny breakfast surprise.
6. Sticky Note Fun: Cover a friend's workspace or door with sticky notes.
7. "Broken" Remote: Put a small piece of tape over the sensor on the TV remote.
8. Upside-Down Pictures: Turn a few picture frames upside down.
9. Silly String: a classic, and always fun.
10. Rubber band sprayer: put a rubber band around the sprayer on the kitchen sink.
11. Change the language: Change the language on a friends phone to something silly, but make sure to change it back.