So, we've selected the next president in the US, and roughly half of us are happy about it, and half aren't very happy about it.
You may find yourself in the bluest of blue states, or the reddest of red states. You may think that your entire office has similar political leanings to yourself, but you may be wrong. Not everyone who voted differently from you is a knuckle dragging throwback or a spineless pantywaist, and it is not terribly politic to assume and say so in an office environment.
I can think of any number of cultures and creeds that are considered "not like us" in various parts of the country. Rural folks, city folks, Muslims, Evangelicals, Mormons, immigrants... Regardless of your personal distaste for a group of people, I would also suggest that you keep disparaging jokes/comments to yourself even though the overwhelming office culture seems to consist of people "like us". Immigrants, people from other US cultures, and members of religious groups aren't immediately obvious, even to coworkers. They may be your boss, your client, your office buddy.
I get tired of this ignorant BS, tired of arguing with it, tired of fighting against it. I many not make a fuss every single time I'm offended. But if I'm in a position to promote/mentor/generally help out someone, it's going to be someone who doesn't piss me off with his/her rampant stereotyping.