A "Coffee Chick" is a girl that will always be willing to know everything that is happening in your girlfriends life. Such as your private sex life, inter-relationship arguments and e.t.c. Your girlfriend's Coffee Chick will address herself as your friend, but always approaches you with a glare.
The vise-versa (a Boyfriend's guy friend), is often referred to as a "Beer Buddy" or "Beer Bud". This friend will listen, but often will be drunk so forgets it the next day. Or her doesn't care.
A gay man, who is best-friends with your girlfriend, is a "Coffee Guy"... same thing.
Coffe Chick: C'mon... Tell me. What happened with John last night?!
Mary: He doesn't want me to tell you.
Coffee Chick: Don't listen to him! I'm your Coffee Chick!
Mary: Okay! Okay! Well... Last night, John sorta... You know.
Coffee Chick: Again?! He needs to... Control that.
Mary: I know. *chuckles.
Coffee Chick: Hahahahaha!
They both break out in laughter.