I clap when I'm happy and I know it 
Since I get to work with preschoolers sometimes, this was EXACTLY my thought!

If I'm performing and am supposed to clap, I'll clap when I'm supposed to. If I'm in the audience and am supposed to be listening, that's what I'll do. I've heard too many audiences start clapping and get so loud that they drown out the music. Either that or they speed up and cause problems.
I don't clap along unless invited. Then in 4/4, it's likely on 1 2
& 3
& 4
& duh... On the beat clapping is for sissies.

cotten