The trick is to avoid the buzzworks. Don’t hit them with any words like communism, socialism, Marx, Engels, Lenin, Soviet Union, China, labour union, etc. Don’t hit them with any theory either.

Just point out how the system is screwing them. Let them talk about their financial issues. Don’t try putting them in a Marxist framework either. Just listen and talk about your problems too. Then ask them what they think should be done about it. THEN, you can start to:

a) either point out how close that is to Marxism (if it actually is, don’t lie or manipulate obviously - but you’d be surprised how many people actually come to the same conclusions as the 2 bearded guys 200 years ago)

b) deconstruct it first and then suggest why you think Marxism offers a better solution (you should probably be prepared for pushback in this case, but as long as you keep the tones low, you’ll be able to have a discussion).

Most people have been conditioned since childhood to react adversely to the buzzwords. If you mention them, you’ll get eyerolls, sighs and defensiveness. If you want to go past that, you need to understand what kind of propaganda you are dealing with first and understand how to not trigger it.

For your dad’s case, I’d say a good starting point would be to show him that he’s not a capitalist, and will never be, no matter how hard he works.