Depending on my mood and the person in question, I may laugh or roll my eyes.
I usually say, "There's a musical for everyone" and then proceed to give examples. If I'm in a sassy mood, I may taunt them by saying something like..."Scared you're gonna like it?"...generally followed by a devious smile.
Luckily, my friends listen to my suggestion about musicals they may or may not like. I also have a talent for being able to "sell" people on shows. I write a lot, so I can describe things pretty well.
"I'm-Not-That-Boring-Low-Ass-Girl?! You better go up at the end!" - Seth Rudetsky to Julia Murney about her Solo CD choice