Challenge
What's one thing you can say to correct someone that believes the earth is flat?
Let's be real here. The whole concept that the Earth is flat is utter bullshit, and people who actually believe this are idiots. We need to do some serious re-education in this country. Stand up and defend the truth!
Frisbee
The moon is round. The sun is round. The other planets are round. Of course, the Earth is just a Frisbee flying through space.