If somebody doesn't know what ironical means they are either a child, ESL or one of the lucky 10000 and therefore don't deserve any disdain?
Too late to choose whether or not to be disdainful, you've already excluded them from understanding you.
It's never too late to learn the meaning of a new word. Why just yesterday I was reading The Count of Monte Cristo, where the author used "felicity" in a context I'd not seen before. Fortunately in my very pocket was a powerful device that includes a dictionary unsurpassed in the history of mankind, and thus my brief ignorance was swiftly overcome! Perhaps the author meant to exclude me? Oh dear...
Ambiguity in conversation leads to problems every day. Leisurely reading is another world entirely.