OK, let's unpack your comment.
In response to my facepalm you informed me that "Not everyone here is American." How should I interpret this?
Option 1: You honestly believe that I don't know this already. For this to be true, I would have to be someone who comes to a fan site for a British band where people have been giving first-hand accounts of shows in Europe and the U.K. for months, yet somehow believes that everyone here is from the U.S., or at a bare minimum somehow believes that the only people who would participate in a U.S. politics thread on such a site would have to all be American. The only way for that to be true would be for me to be a colossal navel-gazing idiot, since anyone with more than one functioning brain cell could not reach the conclusions you would be ascribing to me.
Option 2: You know that I already know that not everyone here is an American, but you're saying it anyway, as if I don't know it. What purpose would this serve, other than intentionally trying to paint me as the idiot from option #1 when you already know that I'm not? And your "I didn't even know you were an American" defense would force this option to be the true one, because option #1 only works if I'm an American who's making incredibly stupid assumptions about the rest of the internet all being American too -- so if you don't know I'm an American, you must still be trying to paint me as a stupid one.
Option #3: You made a broad, stupid remark and can't admit that you misspoke.