It’s so hard for me to use the word ‘ain’t’ like that.  The contraction is for “are not”, so that’s like saying “it are not over” which sounds pretty derpy.

Say it are not so
I will not go
Turn the lights off
Carry me home nananananananananananananananananananananana

 

Anyway, the “it ain’t over until the fat lady sings” quotes come from sports, mostly.  I find it weird that it’d be from sports and not, you know… offensive opera fans.