In Mexican slang, caer gordo means to not like or feel uncomfortable around someone.
No ire a la fiesta por que me cae gordo tu novio / I wont go to the party because I don’t like your boyfriend
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I hope you have learned something new, about the spanish that real Mexicans talk on their everyday life.
If you want to improve your Spanish, I also give tutoring lessons on skype using this page that host many teachers from all over the world, and while I don’t really do grammar, I can help with conversation and doubts about the language. Also, if you are interested in any language besides spanish, there are teachers and tutors for any language there.