Try it with “When the Saints Come Marching In”.
If you clap on saints, then you are clapping on the 1. (“When the” is on the pickup)
If you clap right after saints, you are clapping on the 2.
Try it with Mary Had a Little Lamb. If you clap on “Mary”, you’re a loser (just kidding!)
I clap on the 2 and 4 because 1) it’s the most natural to me and 2)songs sound cooler when they are accented on the offbeats. However, this doesn’t always hold. James Brown is famous for “jamming on the one”, which the accent being on the first beat. But he’s the only exception (who’s cool) that I can think of, but maybe there are others.
My father is quite observant about these things. He was the first to point out to me that white people are more likely to clap on the 1 and 3 than black people. I didn’t want to agree with this (who would ever clap on the 1 and 3!!??) but then one day, we went to a fairly intergrated church that featured lively gospel music. I watched. Sure enough, all the black people were clapping on the 2 and 4. Some of the white people were as well, but others were clapping on the 1 and 3. I wanted to grab their hands and get them on the beat!
I think this tendency is behind the stereotype that whites have no rhythm. Whites do have rhythm, though. It’s just…special.