Actually, a CGN (Stands for Crazy-Go-Nuts, as in CGNU) Thread is used at the old forums I used to be at. We'd go to 500 posts and then lock the thread and delete it. I thought, because I know what they are, I can try to make one.
It's basically a thread in which you can talk about anything, but there are rules.
1. NO SPAM!!!
2. Post length has to be over 3 words
3. No bad stuff, like porn or similar things.
4. Don't do this for the sake of raising your post count. It's just a fun topic.