It's in the running, but my all-time winner is still the comment that dismissed wight lifting for exercise. Called it something like "zero net work" because a rep starts and ends in the same position. I'd link to it, but that might be too mean by dang's standards.

I like threads like this one though. It reminds me not to jump straight to doubting myself when I run into a thread with more-convincing groupthink.

Second only to comment correcting them that it's "cord" and not "chord."