You actually have to listen to the way the word is said.
If "mean" is said in a tone the same way an astonished person would say it, it could mean awesome, cool, amazing, something awe-inspiring, etc. Example, "Whoa, that chick is mean. If you no like get her numbah, I going get 'um." Translation, "Wow, that girl is amazingly hot. If you won't ask her for her phone number, I will.
If "mean" is said in an irritated or angry tone, it probably means irritable, angry, strict, etc. Example, "Ho brah, Mistah Cruz is mean. I gotta stay aftah class today just 'cuz you no like shuddup. Translation, "Man, Mr. Cruz is strict. I got detention because you kept talking and he thought it was me."
I live in Hawaii