Bismilah
Sometimes men extend their hands to shake hands. I just politely tell them that I don't shake hands with men who aren't my close relatives. It's against my religion.
Most of them apologise and say they didn't know. I say no problem, you will know next time. And that's the end of it. It's not a big deal with non Muslims. The problem is with Muslims who do shake hands and can't accept that it's wrong. They are the ones who get huffy.
It's surprising that at times muslims are more in need of dawah then nonmuslims.