This happened (to someone else!) at an opera I was at a month ago. They were not popular.

A similar event happened at an amateur performance of Checkov's "The Cherry Orchard" some four months back. At a crucial point of silent tension, at the climax of the show, a voice from the back said loudly "Doesn't he look like some actor or other?"

A few weeks later, the monthly mag arrived where the director made some rather vicious comments about people who don't know how to behave in theatres. A month after that, the wife of the man wrote in to say he is near-deaf and as a consequence was totally unaware how loud his 'whispered' aside was and how put out she was by the lack of understanding and support for someone who had, in fact, been attending those amateur productions for many years... All in all, an unpleasant interlude for all concerned.