First, you need to be nicer. Calling him "stuck in the past" and saying he doesn't get "basic principles" or "basic OOP" is needlessly insulting. Second, stop

First, you need to be nicer. Calling him "stuck in the past" and saying he doesn't get "basic principles" or "basic OOP" is needlessly insulting. Second, stop blaming him. You're working for him, so obviously he has done some things right and deserves some respect. If you understand something he doesn't, it's your responsibility to explain and educate. If he is "very defensive" then perhaps you are bringing issues up in too confrontational a way. Finally, be patient. Find some code that could be improved with better adherence to Ruby style, work up a changelist that cleans it up, and politely send it to your boss suggesting that you think this style has advantages, would he mind if you fixed it up? Show him how your style has advantages, point by point, and over time you will earn respect.