Yesterday, a friend used "knucklehead" to describe a stranger on Facebook who left a comment under my profile pic that said "You look like a braindead liberal."

I thought "knucklehead" actually wasn't quite a strong enough word, especially because this friend is usually good at colorful verbiage, but I appreciated his and others' defense.
I replied to the guy, "I don't discuss my political leanings on social media so I can tell you only that you're half right."
Because of my job I'm careful not to get too political or partisan on FB. Kelda wondered if the stranger had seen me comment elsewhere. I told her I didn't usually comment politically unless saying things like vaccines are good, which should not be a partisan comment in the first place. (Hardcore Trump-supporting Republicans are going to kill themselves off and be outnumbered by Democrats.)
I also felt OK a few days earlier about replying to a transphobic guy who vociferously argued that a person's gender identity must match their DNA. "Follow the science," he said. I believe human rights should not be politicized either, so I told him that science is never conclusive and why the hell does he care anyway -- someone else's gender identity affects his life in no way.