If it was "a few welsh nationalist hotheads", I'd ignore it as a pinprick - but it was systematic and deeply ingrained in the local psyche - short measures, slow service, the worst products from a display, instant language shifts, random acts of unhelpfulness - you name it I saw it over several visits as a tourist and on business.
Actually, eventually, I did visit again - as a guest at a wedding where I was treated with enormous warmth, friendship and conviviality in one of the North Wales towns where I had spent a week being 'unlucky' a year or two before.
Some of the same people were involved in both my experiences.
I'm afraid that (rather than thinking "oh - I was obviously wrong") that made things seem even worse ... one set of behaviours for insiders, another for the rest is not a good way to live.