If you dont like hearing people acknowledge the FACT that you have a fat wife either drop the fat wife and get a thin or in shape wife or learn to deal with the reality that people are calling it as it is.
It is admirable that you and your fat wife are trying to do something about it, but as long as she's still as the both of you are fat slobs people will think you are fat an no matter what you actually hear will change this. Does it matter if you actually hear them say that she is fat even if the whole world knows that she is fat?
Here is another idea... If you enjoy your wife being fat, try not having a 7th grader as your circle of friends. The more mature your friends are the less likely you will have to deal with hearing about your "fat wife" from them.