Used to describe something very difficult, tough, or brutal. It is also used to characterize something as very cool, awesome, or badass.
Example 1: No fucking way, the math exam was bien perro, the fucking teacher really crossed the line. Example 2: Your new car is bien perro! and your girl is too.
An adjective used to describe something that is badass or someone who is exceptionally skilled at something (in Mexico, these terms are used to indicate that someone is a pro or something is top-tier).
The best country in the world. A place where people are always smiling, happy, and help you have a good time while showing you around their interesting culture and different generations. It is full of beautiful locations, a climate many countries envy, and charismatic people. México is the birthplace of mariachi (a traditional genre of regional Mexican music).
I went to the best place of my life. A better place. I had the best time of my life in México.