4. or when you're scared or desperate and you suddenly say "no mames" just because nervous or something like that and when you say that word is like saying "damn".
A Spanish slang phrase commonly used by Mexicans. Geuy means a jerk (other translations for guey are dude, bro, punk, and more), but young Mexican people use it to adress their friends in a teasing manner. The whole phrase "no mames guey" translates as "You must be kidding, man!" but most people use it refering to its other definitions, such as "Don't fuck with me!" or "Don't give me shit!"
1. Non agressive example ("you must be kidding"):
"Yea, so I just bought a new TV which is flatscreen and HD!"