The cast/orchestra can get there own back. In the early 50's an aged uncle of mine was at a show in London, in his Sunday best outfit. It was a comedy by the crazy gang, a famous clown/slapstick group of artists. He was laughing in the wrong place, talking, generally making a nuisance of himself. The cast told him off, but he went on, so they emptied a bucket of distemper, thats very liquid paint, all over him.
So there is your answer, strategic buckets of paint around the auditorium, for the audience to use on anyone coughing or sneezing. What you do to anyone with a mobile phone that goes off, I don't know. Flogging is to good for them.