The only classical music etiquette I like is that people don't talk during the music. But there are so many rules that seem to come with going to a concert that really only confirm people's idea that the classical music world is uptight. I am anxiously awaiting the moment when I see an orchestra member with colourful socks or dyed hair or a piercing or tattoos or a t-shirt instead of a suit or anything else that shows us they're individuals. I don't understand why people want everyone in an orchestra to look and dress alike, surely it is those individuals that make the music so good? And when people think it's distracting for orchestra members to wear different clothes they really should just get over themselves.
I love going to concerts but I hate that there are set times when you're allowed to clap, and when someone does clap in between movements the amount of sighs and dissaproving looks is absolutely bizarre. Why try to turn both the orchestra and audience into robots? We should embrace our own emotional reactions to music and our humanity, and if that means clapping after a movement then all the better! There's no way that this would actually distract the musicians up to the point where it would hamper their performance - non-classical music musicians deal with clapping/talking/other disturbances all the freakin' time and don't complain about it.
Of course someone's cell phone is gonna ring during a concert, but this isn't the end of the world. Of course people are gonna cough, especially if you mainly cater to the elderly. But does this ruin a concert? Not unless you let it. Sometimes I wish going to classical concerts was more like going to regular gigs, where you're allowed to have fun, dance a bit and relax. I understand that in classical music there are a lot of people very attached to tradition and rules but is it really necessary for the enjoyment of music? I highly doubt it.