My name is Jacob Allen, and I served in the Mexico Torreon Mission.
We had some fun mission lingo. Chincua was what we used for girls. Like the equivalent of fiery dart. Chincua is a mix between chica and inicua (iniquitous). Most places in Mexico used musa (muse). Most popular in other Mexican missions was Frito for a missionary that didn't want to work. We used gandul. Don't ask me where that one came from. I think it's an old word in spanish that no one uses anymore. Those are the two main ones. I didn't use to say fetch until my mexican trainer got me saying it. Not sure if they still say that a lot.
A little bit of parting advice. The Torreon mission used to be the highest baptizing mission in the world about 10 or so years ago. But there was a lot of bad things that went on. There was the age of ANIMO where missionaries would use that word all the time and do anything for a baptism. Even some things that got them ex communicated. Missionaries have a bad reputation in some parts for stupid missionaries that did bad things and stained the name of the church. A lot of the work that we did with our mission president was picking up the pieces and defending our reputation as representatives of Christ. Be obedient and be successful. Don't let your companion, the members, or anyone else with a bad attitude discourage you from doing what you know is right. And that means following the rules. Have the right attitude and have fun.