I am going to have to be maddeningly non-specific for a bit here, for obvious reasons.
I had a job, in which I did work at a place, and other people did work at this place as well.
One of these coworkers had strong political and religious convictions, which is fine. Less fine was the fact that he was incapable of not expressing them, constantly, to any coworker who got anywhere near him. There was no wiggle room, no room for disagreement. He believed that he knew what was right and who was worth voting for and anyone who disagreed needed to be argued out of that position, informed why their opinions were wrong, and educated about which talk-radio shows they should listen to.
I told him many times to stop, not just for my sanity but because I knew for a fact that he was permanently damaging his own career, but he would not stop. We reached a point where if I even made eye contact with him he’d smile like he thought he was a naughty boy, say, “Hey, you know that subject we can’t discuss at work?” Then he would talk about it at length over my protests.
Finally, I made up the card below, which I laminated and carried with me at work. (The other side of it was filled with important phone numbers and other information I needed on a daily basis.) The next time he brought up the forbidden subject, which was very early in the very next shift I had with him, I pulled it out and read it aloud.