Such as “money can’t buy happiness” or “what doesn’t kill you makes you stronger”. Generally a false adage or something like that. All I could think of was “fallacious bumper sticker” which just sounds stupid.
For example someone says “you can’t teach an old dog new tricks” and you might say “that’s a questionable phrase.” or “I doubt the validity of that platitude”. But is there something specific to label it as, i.e. “That’s a [insert word]”
In this case, what you are doing is to purpously misunderstand the figure of speech by taking it literally. This phrase isn’t actually about dogs, but it’s about the fact that it’s really hard to change someones mindset or habits if they’ve been doing it for long enough.
So saying “Well, I once saw an old dog that learned a new trick” completely misses the point here.