LW2, I have COPD and am on oxygen 24/7, and cough a lot.  If I had to get up & leave, I'd never sit down during most outings.  While I do cover my mouth, I often get "stares," not only in restaurants, but grocery stores, as well.  I just simply explain to those close to me, who look concerned, that the COPD makes me cough--my lungs have to be cleared out in order for me to breathe and live.  And I am not contagious. That usually "clears the air" for the other diners/shoppers.