My parents were never aggressively militant about this, but we all got the message: avoiding "the appearance of evil" meant no coffee-flavored anything, no cooking wine, no herbal teas even.
Once they invited another couple they knew to come to our home for dinner. This couple was Jewish and apparently didn't know anything about Mormonism, so being the polite people they were, on arrival they presented my parents with a bottle of wine. I remember my parents being quite flummoxed over what to do with the thing; they didn't want to serve wine at their table in front of their children, even just to their guests, so they ended up explaining to them that Mormons didn't drink or serve wine, and their friends were quite embarrassed as a result. But my parents never disposed of the bottle either, for some reason. It sat in a kitchen cabinet for years afterward.
After I grew up and realized there were other versions of the Bible besides the KJV, I began to see the ridiculous logical conclusions of my parents' (and most Mormons') interpretation of what it meant to avoid "the appearance of evil." I looked at other Bible versions and found that the KJV is unique in using that phrase, whereas every other version I've found says something like "avoid every kind of evil."
In short, the Mormons have taken one phrase from the one version of the Bible they accept as authoritative and twisted it to mean something completely wrong. If they are right, then Jesus did wrong by hanging out with corrupt, sinful tax collectors and prostitutes and everybody else the Pharisees criticized him for associating with, because by spending time with them he was somehow sanctioning the idea that they were good people, right? God forbid anyone should do that, treat "sinners" decently. So the Mormons make themselves just like those Pharisees.
Yet for some reason, they refuse to see this error and contradiction. My TBM dad does his best to be a good and decent person but for some reason he just can't get past the Mormon spin on this. I've had this discussion with him and he simply refuses to acknowledge that the Mormon interpretation of the KJV phrase may be wrong, or at least misconstrued. He thinks their version is "spiritually safer," regardless. Sigh.