They requested me to attend the meeting, however, I am honestly CBA today.
It is a rain and it is cold; I just can not be bothered to go out.
Those instances demonstrate the use of the phrase to express hesitation or lack of enthusiasm without going into much detail. It is a shortcut of explaining to others that you are not in the mood to do something. The tone is informal and therefore it should be applied to your friends who know your style of communication. Know more about what does cba mean