Conservative and liberal are entirely opposites, about that we can all agree. However, a conservative is not entirely the opposite of a liberal. At least not in the context of American politics. Calling someone a liberal or a conservative is very different than calling them liberal or conservative. A liberal is specific. A conservative is specific. Liberal and conservative are both relative terms.
To say that I am conservative is not incorrect. In many ways I am. My manner of dress and my belief in traditional practices and family values are very conservative aspects of me. On the other hand I am also very liberal in many aspects of my life. I spend money like it's water, eat the best no matter the cost, and accept the lifestyles of others no matter how alternative they may be (so long as they don't infringe upon the rights of others). But none of these things gives rise to calling me a liberal or a conservative.
Don't take this the wrong way. I have many political views that cast me as a conservative. I also have many views that cast me as a liberal. However, all of these views come from a belief in letting people do as they please so long as they do not get in the way of others doing the same. In this respect, my political views are extremely liberal even where they do not make me a liberal.
So, when I claim to be very liberal and people respond that I am nowhere near to being a liberal, I am both proud for myself and sad for their ignorance. A liberal in this country desires the expansion of government programs. At least that's the largest difference between them and me. When I ask how I am conservative people talk about my belief in an individual right to protect one's self and one's property (ok, so they say "right to bear arms"), and my belief in small government. Because of these things, people want to label me a conservative. To me this is insulting because it implies that I support any form of governmental control over the individual. If you have read anything I have written, or know me at all, you know this is not the case.
Call me liberal, call me conservative; call me Ishmael. I don't care about that. But when you force an inaccurate identifier upon me with that all-important "a" that's when I take offense.
I tend to think that pigeonholing people into one thing or another is unfair. It's easy to classify Rand Paul as "a conservative" but it doesn't really describe the entirety of his beliefs. There are few people who truly fit a single label. President Obama could be classified as "a conservative" if you look at his record on restricting civil liberties and his hawkish stance on our foreign affairs. If you want to classify yourself as "a conservative" or "a liberal" be my guest, but it's lazy. There is more to you, just like there is more to President Obama, than either of these labels can cover. And if not, you should probably stop talking politics until you grow some ideas of your own.