For most of my childhood, I heard the following sort of thing on a regular basis: “HAHA did you just say SAL-mon? Don’t you know it’s pronounced SAAAAAAAA-mon? DUH.”
There are basically three appropriate responses when someone mispronounces something. One is to politely say something like, “Hey, just so you know, that’s pronounced SAH-mon.” Another is to say nothing but use the word yourself and pronounce it correctly. The third is to realize that you do, in fact, have the option of just letting it slide and not playing English Police. They’ll learn eventually; you don’t need to be their personal savior.