From time to time people post messages asking for places where one could feel at ease dining alone. I've always found this a little puzzling...I think with a modicum of self-assurance, one can eat anywhere alone and not feel uncomfortable. And restaurant staffs with any degree of professionalism will treat a single diner in a courteous manner.
So I thought I'd try asking the opposite question. Are there any noteworthy restaurants where you have been made to feel distinctly unwelcome as a single diner?