I had an acquaintance/friend in college who was always trying to get me to join the Anime Club. He occasionally would tell me about animes he really liked. If I said, "Wow, that sounds really cool!", then he would invite me to the anime club--which I didn't want to join because it was full of social lepers. So instead I would listen with apparent polite disinterest, and try to change the subject. Sometimes it's easier to pretend you just don't "get it," than it is to bluntly say, "I don't want to be associated with this kind of thing, please don't bring this embarrassing subject up anymore."