It seems to me that there are obvious distinctions to be made. For instance, I dislike being called 'Welsh', since it means 'foreign' and my ancestors have, as far as I know, been here since the first settlement. 'Taffy' is an unpleasant attempt to imitate someone saying 'Dafydd' with a strong accent. 'To Welsh' is almost exactly equivalent to 'to Jew'. When I discuss political issues with right-wing English, they inevitably tell me I shag sheep. The first, 'Welsh' is offensive', but most people don't even know what it means; 'Taffy' is always unpleasant, roughly equivalent to 'Nigger' in force, but most English like to pretend it is just jolly fun, based on, of all things, the river Taff, as if they knew where anywhere in Wails might be; similarly, they pretend that 'to Welsh' is really about some Prince of Wails, at some time or another; the bit about sheep is always deeply racist, and prevents serious discussion - it is their way of escaping into a slanging-match. So which would it be 'PC' to ban? Obviously real Nazis would keep every possible way to be offensive, but I'd suggest that only the last should be banned, and its perpetrators jailed for attempts to cause a breach of the peace.