I did not know "worst thread ever" posts aren't allowed. Live and learn. Darn.
If you're on good terms with somebody and you say "worst thread ever" with a wink, it's probably fine. It's when the comments seem to be disrespectful, mocking, or vitriolic that there's an issue. Calling somebody's thread "moronic" or "idiotic" falls into that category.
If people think somebody's thread is stupid, they should either voice their disagreement civilly, or move on. For other examples of stuff we ask people to stay away from, see
here.