Party politics (in the UK). I don't have some "tribal" loyalty to any one political party, but the vast majority of people I've had the misfortune to discuss the topic with do (including my entire family, they've been voting for the same party for generations). I cannot understand always voting for the same party year after year, decade after decade without any thought as to how the parties may have changed or which one is best placed to govern under whatever the country's current circumstances happen to be.
The arguments people come out with tend to boil down to stereotypes, woefully out of date examples of a previous incarnation's activities (which often happened before the person was even alive), vague conceptions of parties' ideologies that haven't held true for generations and often, at the end of the day, "because it's what I've always done."
Maybe I'm a bit odd, but I consider it every voter's duty to read the damn manifestos of each party at an election, to research the candidates in your area, do your best to see through the spin on *all* sides, not just the bits that suit your existing biases, and to do your utmost to ensure that you make an informed decision. I find it staggering how little so many people know about the current policies of the parties they "just know" are "right."
I don't have much of an opinion on the American equivalent, because from what I've seen the two major parties actually are substantially different and relatively consistent. The same is not true in the UK.
I've voted Conservative, Green and Lib Dem in various elections in the last couple of years alone. I stand by my vote in each case, and would be happy to justify each choice I've made. But like I said, I've learned to avoid that sort of conversation
*breathes* I feel so much better for letting that out. Cheers OP!