As some have commented, the rule is show respect, not to fabricate feelings. You don’t have to go overboard. Just stick to the basic rules.
This can be quite hard to do when the parent doesn’t show respect for you. And in our era, this is not uncommon, particularly in New York.
So practical advice will depend on exactly what you are experiencing. If the person is just a buffoon, that’s one thing. If they drive you crazy or push you around, that’s another.
Generally, keeping to yourself is helpful. It’s amazing how much better we can along with people when we don’t talk.
But why do it? It helps the world run better. You need a certain order and hierarchy. Even if a local rabbi is foolish, we should treat him with respect or else you have chaos in the shul.
Also it builds character to suffer a fool, and just keep the mouth shut. You’ll get smarter while they get dumber. In the end, you win.
Another thing to consider is some sympathy for the parent. (I’m not talking about a highly abusive parent.) We live in the end of days. The world is nuts. Your parent likely suffers to earn a living and may have been mistreated his or her whole life. He or she might not have had good role models. There are many possibilities.