Speaking proper Spanish
Each time I'm in Spain, I'm tempted to speak proper Spanish. In the end, I always do the bare minimum.
The official language in Mexico is also Spanish. However, it has evolved since it was “forked” many years ago. At some point, we should start calling it “Mexican”—half-jokingly, I already say I speak Mexican rather than Spanish, and people around get quite confused.
I would say the overlap between Mexican and Spanish is greater than 95%, we can understand each other pretty well. However, that 5% difference gives room for funny misunderstandings. When I point this out, some English speakers ask: “is it like American and British English?” ... sorta.
Pronunciation differs. For instance, in Mexican, 's', 'c' and 'z' are pronounced the same when these letters appear in the middle of the word. So, casa and caza, same pronunciation. Gazillion of other words, same sound in Mexican, different in Spanish.
Granted, that's an oversimplification in Mexican. If you pronounce it as in Spanish, you already have more information about how the word is written. If you do it as in Mexican, you have to memorize it.
Then there are words with exact same pronunciation and spelling but different use. One of the most annoying examples for Spanish people is the verb “coger”. One meaning of that word is “to take”, so, you can “coger un taxi”, “coger un elevador”, “coger la chaqueta”. In Mexican, the official meaning is exactly the same, but the slang meaning—and the most used— is “to fuck”. For the Mexican ear, Spanish people say “to fuck a taxi”, “to fuck the elevator”, “to fuck the jacket”.
Also, the word “chaqueta”, a jacket, in Spanish. Mexican slang? A session of self-sexual-pleasure (masturbation).
It is hard to believe this language's evolution occurred by accident. Someone, somewhere, somewhen thought this through. He/She/They mess things up on purpose. That's my hypothesis.
The Spaniards destroyed the cultures they found when “discovered” America. Well, we will destroy the language you
taught imposed on us. Something like that. Maybe.
Even when words are reused without any spicy messiness, things get confusing.
To avoid confusion, a Mexican would say “tortilla Española” and a Spanish would say: “tortilla de maíz Mexicana”. But when there is a group with a mix of Mexicans and Spanish, we tend to simply say “tortilla”, leading to some very funny semantic issues.
And so on, and so forth.
And I've spent enough time in Spain to attempt to speak Spanish. But that wouldn't be me. I am not Spanish and don't speak like that. Even if Spanish people consider Mexican an improper Spanish, I still speak it anyway. Otherwise, it feels I am pretending to be someone else, like acting a character. It would be really weird.
That said, I try to purposefully choose the most commonly used words in a particular region or country (except coger, that one I still avoid, there are plenty of synonyms). While in Spain, I use “autobús” instead of “camión”, “¿perdona?” instead of “¿mande?”, “me pones X” instead of “te encargo X” (that last one is used in bars), et cértera.
The rule of thumb is that, as long as “my way” is not considered offensive in the hosting culture, I will do it my way.