My thoughts.
Sometimes I have a dry cough. I should do the cough into elbow thing and do so but were I to have a senior moment and forget, I suggest that a concerned passenger catch my eye and mime coughing into elbow with a smile. I should return the gesture with a smile and thumbs up.
It's also easy onboard to leave the table if you have a coughing fit, say from swallowing the wrong way, and go outside, cough up a lung and return when back to normal.