Pedro was never particularly polite though, it's not his character. He is a cunt as he puts it himself. I love him because he understands he has flaws, and admits to them. Even then, he still tries to do good. He is a very human character.
Also, i was under the impression his hatred for the argoi has to do with identity fraud. Pedro comes from the Argos Panoptes lineage, the thousand-eyes giant. Nikos and his people, have been taking on that name in order to torment Asterion the prisoner. This is done as an allusion to the tale of Io and Panoptes. (Even their scales have eyes like patterns). So that was my interpration as to why Pedro would be inherently displeased with Nikos, he is usurping and sullying his family name.