No one ever says CA, Amy; it's only written. You hear it in your head as California, not "see ay". The only acceptable way to refer to CA when speaking is California. Cali is unacceptable in any context.
In a perfect world, it would be added to the banned words list. Seeing those four little asterisks (and the confusion/consternation of those who tried to type it) would make me so happy.
I'M ON A ONE-WOMAN CRUSADE