"They don't even recognise the rules of argument." You've hit the nail on the head, there. That's why it is so frustrating!
Honestly, you lost him at Lenski. He doesn't understand it and doesn't care to. In fact, he's likely just checked out of the argument as soon as he hears something he doesn't understand. He's soley on defense at that point.
Hey, you got some good licks in. Don't be so hard on yourself! If catching you being frustrated feels like a feather in his cap, let him have it. Frustration with ignorance of both the subject matter and the ability to debate it is a perfectly appropriate response from an educated person!