My dad is immensely purposefully dense and insists on talking about things people expressly ask him not to....
I will ask him 7 times not to talk about a certain thing. He will continue doing so using bullshit phrases like "I'm just saying." Really? I know you're just saying, and I'm just asking you not to say that. Talk about anything, everything but that.... His latest subject is the difficulty of lawyers "getting paid by clients, and how he can't believe it." He'll throw out the same over simplistic suggestions that I have repeatedly explained to him will not work. Also I love dwelling on financial difficulties in my profession in what little free time I have as he drags it out long after I've repeatedly requested he stop. For the love of god, and after how many requests, change the topic.... Don't explain to me why you're still talking about it. Nothing you can possibly say will change the fact that I don't want to talk about it after I've asked you repeatedly not to talk about it....
Eventually, after repeated polite requests, I have to be so damn blunt as to tell him to shut the hell up about it. Naturally he is hurt by this, but at that point I just don't care/have any other option.
It is next to impossible to get him to change the subject to anything enjoyable, remotely. I'd settle for a boring but neutral topic. He is so damn stubborn and prone to interrupt anyone he talks to (largely limited to me, cause no one else will take his bullshit, at all). He likes woodworking, I attempt to talk about that. I'm honestly not knowledgeable enough about cars to have a conversation with him about those but I've tried to repeatedly just to change a subject.
He doesn't want a conversation with someone, he wants to lecture at someone about an unwanted subject proving his delusions of grandeur.... [facepalm] He never listens to what anyone says, because he's too busy thinking of what he'll say, which by his definition is always more important (though he will never say that).