The reason a Latino would normally use the word is because of US culture grouping every Latino as a Mexican. Thus hate grew towards the Mexican because they feel Mexico represents nothing of them and their home country. Others feel when they are called "Mexican" they are seen with the usual stereotypes of a Mexican.
John: "What part of Mexico is that?"
Juan: "Shut your racist shit up! I'm not a Mexicaca!"
Pedro: "Mira ese Mexicaca." "El piensa que es la gran mierda!"
translation: Look at that Mexicaca. He thinks he's the shit!
Pablo: "Simon!" "Sucio culero." "Por eso odio esos Mexicacas!"
translation: Yeah man! Dirty faggot. That's why I hate those Mexicacas!
1. It's a demeaning term that other Latinos use when they talk about a Mexican. Caca in Spanish means shit. Most Latinos think they're better than Mexicans, and see Mexicans as inferiors.
2. The word mexicaca originated in the 70's or 80's as a racial slur against Mexicans.
I can't stand that mexicaca music. Mexicacas are peasants and have no class.
Javier: Mexicacas don't look like human beings, dude, they look like they're dwarfs from another planet. ha ha