Well, to take a different approach than the unanimity above, there are ways you can share your dissenting political views and minimize the drama.
First off, tone is extremely important. "Hey, I think you guys are politically inept, I'm a Libertarian" is probably not the best way to go, for an obvious example. Take a neutral tone at minimum, perhaps even go for respectful, but at all costs avoid getting into a fighting and arguing tone. That just leads to excess dramatics, so it's better to just avoid it.
It's also important to deliver said information at a reasonable moment. Just barging in on an unrelated conversation with "anyway, I'm a Libertarian" would be silly. Wait for some relevant (ie political) topic to come up, then share your actual views. Honestly, if you want to avoid people being ridiculous about your political stances, don't use a label first thing. Saying that you identify with a particular political party comes with so much baggage and nonsense that unless you agree with 100% of the party's positions and goals then it's not worth it most of the time. Explain what you think about various issues on a one by one basis, then if someone presses you to claim a party you can either say it straight up or go with something like "I don't stick exclusively to any party, but the Libertarians are the ones that come closest to my own opinions." When you display reasonable thought like that and show you're not just another turd who just picked a party and votes for it without actually understanding the issues, then you're less likely to get shit for your opinions. People can be blindly stupid about politics once it becomes a discussion of party vs party rather than a discussion on the actual issues that matter, so best to avoid that.
Oh, also, that's a vital precursor to any kind of political chatting or decision making that most people skip: actually research and examine various issues before talking about them like you know what's going on. Seriously. Saying "I don't know, I haven't looked into it much" is a far better answer to annoying questions than just taking a stance blindly because the party you happy to like for other things happens to lean a certain way on the other issue. For example, in the United States there's this really funny thing going on in the states colloquially called 'the South' where most of them go for the Republican party because that's the Christian morals and family values party. There are folks who are well below the poverty line and dependent on entitlement programs like food stamps and disability benefits... and then they talk about how entitlement programs are awful and need to be cut hard, because that's what the Republican party says, and they vote for people who campaign on platforms of cutting entitlement spending. Don't be one of those people. Look into various issues for yourself, ignore what various political parties say on the matter, and come to your own decision. You'll get a hell of a lot more respect in political talk when you prove that you actually know what you're saying and have investigated issues, so if you can do that when talking to your parents about politics then it'll be harder for them to blow you off as an ignorant kid who's just rebelling and picking an antithetical view to their own.
So, in short, mind your tone, deliver the information logically, and actually know what you're talking about. You're not going to be able to help the angst that comes from having differing views, but this is what you can do to mitigate it.
