Do you mind me asking why they think you're bad?
I don't mind... I am curious to that as well (well, I think I do know why). I think it has something to do with the way I live my life and how I put stuff in perspective. And actually their son (at least my friend, not directly his brothers) is a bit like me. We get along perfectly and have a lot of the same views on stuff, it just happens that his parents feel that I actually help and acknowledge "his" views, because they're similar to mine. Thus they feel I'm solidifying his opinion towards stuff they feel isn't "normal" (or in general isn't their idea of right/wrong).
They actually thought that I used drugs and I sold their son drugs (and thus got him on it), while actually... it was the other way around.
Another thing, to just put in perspective his parents; his mom wants to kick him out (he moved back in with his parents due to mental health issues; and in the time I haven't spoken to him, he got an official diagnosis on having aspergers alongside other stuff) because she thinks that adapting little things around the house (in regards to daily life; stuff he's having a hard time dealing with) is to much of a hassle. So his parents are a bit of the "it's my way or the highway"-type of folks.
But I don't hate them for being that way. I do have some resentment towards them because they're not honest and upright when my name gets around in a bad way in their conversations. When I was at his place some time ago, I told his mom "listen, I don't care if you like me or not, but do not talk behind my back, if you have a problem with me, tell me, instead of conjuring up all kinds of silly stuff for which you presumably have no proof". And she stated that this never happened. However, I told her "Fine... so you're calling your son a liar, your other son a liar and a friend of that other son a liar?" She got kinda stumped. When I just finished my sentence, the doorbell rang and that friend of his brother was at the door, so I said.. "oh great, let's ask him while he's here". And he kinda confirmed that my name got around there. I don't care what people say about me, as long as it's true... but do not say that you never talk about me, if you actually are.
It's stuff like that... probably also having this direct approach which gets to them, because they can't enforce a "my way or the highway" principle on me and I will test them for it each time my name is involved.