Refusing service because of political party.

[johan]

I'm thinking that in reality, if a person consistently threw out black/gay people, they'd be considered to be discriminating even if they said these people all just happened to annoy them. 

And you'd be right. If someone was consistently denying service to all black or gay people, it wouldn't be difficult at all to prove discrimination in court regardless of their claimed reason.

But I guess if you consistently throw out democrats, then that's okay, legally speaking. 

True. Political affiliation is not a protected class.

However, you could claim to think that all gays are democrats...?

Well you could try it I suppose. But it would be an extremely weak legal defense and I doubt any judge or jury would buy it.

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I don't personally see a difference between being a douche over religion and being a douche over politics.

You might not, but the law does.