Whilst I have spent my life abusing the Welsh and generally using them as the butt of jokes, I have more recently come to amend my views. I was raised in Chester, an English town dating from Roman times, on the Welsh border, so anti-Welsh feeling was more a part of my up-bringing than maybe some others from Britain. It was the Romans who named the Welsh for us, I understand that "Welsh" is the Roman word for "foreigner" so they were just the enemy in a general sense rather than a particular race.
That aside, there has of recent times been a popular movement towards embracing the ancient roots of the people of the British Isles, strange as most inhabitants are descended from anywhere but the islands (once you go back a few hundred years). This upsurge in celtic jewelry, and interest in the remote past should have meant that the Welsh became a popular section of society, as they are the true descendents of the poeple who tied those knotwork patterns, and gave rise to King Arthur etc. Instead their modern image as the lowest strata of the United Kingdom persists, unfairly really.
To someone from another country I should explain that every nation has the section of their populace that are made fun of in national jokes, be they the Newfoundlanders or the Flems. In Britain that role is played out by the Irish, who are set as stereotypical foolish rogues, incapable of the sensible decision, inexorably drawn to the comic outcome. As such they occupy an affectionate (more or less) position in the national psyche, the Welsh on the other hand are more liekly to be made the butt of jokes involving bestiality. No one said life was fair.