The most well-known story says that in 1415, people from Porto won the name of “tripeiros” for having given away all the meat of the city to the armada of Infante D. Henrique who sailed that year from Porto to conquer Ceuta, our first stronghold in Africa. What was left was tripe which is what people ate.
If you’re familiar with Portugal you may have heard the nicknames given to the people in the main cities: the people of Lisboa are called Alfacinhas (little lettuces) and the people of Porto are called Tripeiros (tripe-eaters).