Presumably some other members of the audience had a drink too, and it was only a small section of the audience who didn’t know how to behave. I have observed parents whooping and yelling at infant nativity performances, nothing to do with drink, just the lack of understanding of some parents. They watch talent shows on television where this behaviour is seen as normal- in fact the audience is hyped up to behave exactly like this. Not much we could do, except mention in a newsletter prior to the performance that we would be pleased if parents could applaud quietly etc. I don’t think the presence of alcohol has much to do with it.