Ñero

This expression is a pillar of Chilango slang. The origin of ñero (GNE-roh) is the word compañero, which means companion, mate, somebody in your same circumstance. Ñero was first used as a short version of compañero. Later on, ñero became a reference to the people that used that expression: mostly uneducated urban youngsters. Finally, since those ñeros are tough and bold, ñero became an adjective to convey those characteristics. If something is said to be ñero, that means it is tough or harsh.

Example:

Paramédico: ¿Qué tal estuvo el concierto?

Matías: Se puso super ñero el slam.

Paramedic: How was the concert?
Matías: The mosh pit got really harsh.