One of my cousins came with me to church a few years ago (when I was still a teenager). That Sunday happened to be the day the young men and women sang “The Army of Helaman”. I don’t know if my cousin thought we were did a good job or whether he was just being polite, but when we were done, he started clapping.
It amounted to maybe three or four claps because it didn’t take him long to he realise he was the only one. He isn’t a Mormon and not clapping in church was something we took for granted and forgot to tell him.
Maybe we should have a sign outside: Visitors welcome. No clapping.