It isn't uncommon for more anglicized Mexicans to take a dislike to other Mexicans. A lot of self-hatred in that culture; I'm sure routinely being shat upon by other Hispanic peoples (Cubans, Puerto Ricans, etc.), in addition to whites, plays a part.
This, of course, is neither defense nor justification for Mario, for every breath he draws is a foul stain on the entire human race.