Fights

Don't you hate it when parents fight?

My stepdad has this.. issue(?) where everytime I do something wrong, he thinks about it after it's delt with all the time, and then he'll think of something that he can use against me for the same reason, come home/back/up to me and start the argument all over again so that he can say that one thing, and it drives ´me and my mum crazy.

Like today - I downloaded a song illegally, my mum saw and had a go at me, so I stopped, and then my stepdad went out. He just came back, and has immediatly come to me asking about where I got the music that's playing off the computer, so I told him it was playing off youtube (Because it was) and then he's all "Show me." starting the argument again, and he wont back down untill I show him (Which I didn't). My mum told him to leave it, and he starts coming out with some bullshite about how he's worried about where I got the song from, and my mum tells him to shut the hell up because it's all been delt with and he doesn't need to bring it up again etc, and he just looks at her like she hasn't even said anything, and when they're done arguing, he acts like nothing happened at all, making my mum even more annoyed.

Why does he have to be such a fool?! Every single day something like this happens, and it's not fair on my mum, because she's always stuck in the middle. :(