How to explain mirror touch to people without freaking them out or them thinking I'm lying?

Basically I'm spending time with various people who want to watch shows/movies which either trigger my syn or might trigger it, and while I can usually get out of watching horror stuff with "I have a really bad phobia of blood" and pro boxing shows with "I hate violence.", many people forget about that one scene in a certain movie where the guy gets punched. Or they think a movie where a girl eats poison and throws up is fine because it's not violent and there's no blood. I've tried to explain to my family how I can feel it when stuff like that happens but given their total disbelief and mocking, I'm not exactly looking forward to trying to explain it to acquaintances who probably already think I'm odd.