Simple as that -- make a question and the other person gives a stupid answer, also the person who answered needs to give a new question.
Example:
Post #1:
Q: Why can't humans fly?
Post #2
A: Because of the chickens, so they don't run through the salad.
Now you start.
Whats 2+2?
5
What's the color black.
potato, how many o's are in o.