[PaperBagger'14]

Here's a message to make fun of a bad thread on a message board:

Subject: Wow, this thread really took a nosedive...

"Guys, I think we need to officially declare this thread the 'Official Trainwreck of [Month]'.

First, [User1] brought up [controversial topic 1], which predictably exploded.
Then [User2] decided to chime in with [outrageous opinion 2], and all hell broke loose.
Now we're arguing about [completely unrelated topic 3], and I'm pretty sure we've lost all semblance of reason.
I'm honestly surprised we haven't resorted to posting cat gifs yet. Maybe that's the only way to save this sinking ship."

Optional additions:

You can add specific, humorous quotes from the thread to further emphasize the absurdity.
If there's a particularly egregious post, you can gently (or not so gently) mock it.
You can suggest a new, more productive topic to steer the conversation back on track (if you're feeling charitable).
Important Note: This is just a template. Tailor it to the specific events of the thread for maximum comedic effect. And remember to keep it lighthearted and good-natured.