in my experience, the more polite you are, the more likely you are to get punched in the face

If you are in a venue where politely asking someone to keep it down, results in them actually responding, you generally don't need to ask. You are among conscientious people to begin with.

For the most part, about 99% of the time, the whole point of drawing attention is waiting for someone to politely ask them to turn it down. And it isn't so they can respond in kind.