Gin martinis should always be stirred as it's the gin that bruises. Vodka martinis should always be shaken as there are no botanicals to agitate. As far as vermouth, you can technically bruise it in a shaker which is why it's best to just rinse the glass in vermouth instead of directly mixing it in the shaker.
I would say that applies to everyone. I have occasionally pulled some peated Islay scotches on people to get a laugh, but most are not ready for one right off the bat. They are the deep end of the scotch pool.