That was probably me. I don't think I handled the situation particularly gracefully, but I really didn't want to continue that conversation, and I couldn't see whether the person in question was wearing a crocker's rules tag.
I don't remember my actual words, but I think I wasn't trying to go for "nothing could possibly convince me", so much as "nothing said in this conversation could convince me".
It's still more graceful than the "I think you are wrong based on my heuristics but I can't tell you where you are wrong" that Pablo Stafforini advocates.
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.
Notes for future OT posters:
1. Please add the 'open_thread' tag.
2. Check if there is an active Open Thread before posting a new one.
3. Open Threads should be posted in Discussion, and not Main.
4. Open Threads should start on Monday, and end on Sunday.