You don't. Depression is something that if people don't understand it, they usually won't understand it unless they go through. I told my mom that I thought I might be depressed. She told me that I was just bored and so much of a pain that she sometimes regrets that I was born. She's a doctor. She's well aware of what depression is. People like that will not ever understand it. It's a waste of time trying to teach her.

But I don't want to damn your relationship with your dad. I hope you realize that those things he says to you is very damaging and abusive. I guess the only way you'd be able to get him to understand is to tell him that you don't need to have a reason to be depressed and then explain what it is from a medical standpoint. Then you could talk about the feelings surrounding it and stuff like that. Of course this requires him to be willing to really try to understand and be able to recognize that his mindset is wrong.