The concept is too simple, almost like Ask A Stupid Question, Get A Stupid Answer.
Here's how it goes:
The first poster askes a question, like
"Why Did You Forget Your Homework?"
and the poster after makes a witty excuse, like:
"I forogt to remember."
You can't just add any question, it must be able to have an excuse. Anything like "WHy do I like lettuce" to "DO I smell bad?" doesn't have an excuse attached to it. Follow my top example. The question is what a teacher at school would ask, and the excuse would be what a student usually says. Think of it as a teacher-to-student relationship you're thinking here.
So, I'll start:
Why are you late?