In Argentina and in some other places in Latin America ´gallegos´ (that is people from Galicia in Spain) are what Polish are in the US. For us if there is a joke about not being bright, it involves a ´gallego´.
But this is the first joke about Gallegos that I have seen in English (thanks Bi!) and I think is because you have to know English, Spanish and how bad we (Spanish speakers) may pronounce English in some occasions. Basically, it is a bicultural joke that goes like this....
Three men, an Italian, a French and a Gallego went for a job interview in England.
Before the interview, -they have to compose a sentence in English with three main words: "green", "pink" and "yellow".
The Italian was first: "I wake up in the morning. I see the yellow sun. I see the green grass and I think to myself, I hope it will be a pink day."
The French was next: "I wake up in the morning, I eat a yellow banana, a green pepper and in the evening I watch the pink panther on TV."
Last was the Gallego: "I wake up in the morning, I hear the phone "green...green...", I "pink" up the phone and I say:... "Yellow?"