I learned this one the hard way.
Never wrestle a pig. You both end up dirty, but the pig likes it.
The Bible says it this way in Proverbs 26:4 “Answer not a fool according to his folly, lest thou also be like unto him.”
Once it is realized that someone isn’t sincere in discussing a matter, it is time to walk away. Nothing is owed them and if you continue to argue, it ends up costing you.
Fools abound.
Let them alone.
Joel Stiff's Adventure 
i believe there is a full-blown devotion (although full-blown says sermon and not devotion) in that thought!
I’m not usually known for my brevity.