When somebody thinks that you really give a fuck about what they are saying when you dearly dont.
Rude Girl: You better watch what you do before i have my boys beat down on yo ass cuz im frum fifth ward baybay i dont play nice girl: Nobody asked about your life story with yo brainyass.
1. describes a very smart person
2. A forehead wrinkle (aka worry line)caused by too much deep-thinking by the aforementioned very smart person
plural: brainies
definition 2: Check out all the brainies on that dude's forehead...talk about a prime candidate for a facelift!