Some people don't like to talk about how they plan to vote. Ask them how they plan to vote and they look at you like you'd just farted in church.
I respect their right to privacy, but I'm curious about why such a public, civil decision is regarded as such an intensely private matter. Democracy, after all, relies on citizens being willing to discuss and negotiate such things, and that great and necessary civic conversation is not easy to conduct if we all decide to treat it as a secretive, private matter. This ain't personal hygiene — this is getting together to decide how we are going to live together as a country.
Having secret ballots is a different matter. Secret ballots are necessary to protect voters from potential coercion, intimidation and retribution. Those same concerns may keep some people from even wanting to discuss their voting preferences. The fact that such fears may sometimes be valid does not speak well of the state of the union.
For some people, the refusal to discuss their vote may be a way of signifying that voting is a serious matter. Maybe it's something like the way devout Jews avoid speaking the name of G-d. (Most Americans, of course, have no problem saying God's name. If you want to know what it is that Americans worship — what we regard as sacred — start asking people what their salary is.) But this attitude also seems misguided. Voting is important — too important not to talk about it.
Some people, of course, are probably just trying to avoid a potential conflict. I understand this too. That's why I never talk politics with my dad. But then again, the reason I avoid the subject with Dad is because I already know exactly how he intends to vote, not because we're coyly pretending that our voting preferences are some intensely private secret, like birthday wishes that won't come true if we speak them out loud.
Closely related to the desire to avoid conflict is the desire to avoid taking sides and therefore to avoid the chance of being wrong. This is, I think, what motivates many of the supposed "undecided" voters. They remain on the fence not because the choice is difficult, but because as long as they're perched up there they don't have to worry about coming down on the wrong side.
For others, I suspect, the taboo against discussing how they plan to vote arises from some notion of being "polite." To discuss politics, they feel, would be impolitic. And so they come to regard politics in roughly the same way that Victorians regarded sex.
But this is all speculation. I don't really know why this subject is such a taboo for so many people.
Got a theory?