NGBF 

Not Gay Best Friend.
A friend that everyone things is gay but isn't actually gay.

"Is Mike your GBF(gay best friend)?"
"No he's my NGBF."

NGBF by The5thman October 25, 2017

NGBFF 

Not goNot gonnna be best friends forever

This means you are bet friends but you don't think it'll last.

Sandy: I don't know about our friendship.
Mike: What do you mean?
Sandy: Well, we're definitely NGBFF.

NGBFF by born to ride x3 June 10, 2008