I cross my arms when I'm cold.

I cross my arms when I don't have pockets and can't figure out what to do with my hands.

I cross my arms when I'm trying not to fidget.

I cross my arms when my lower back hurts because I can push my ab muscles against my arms and stretch without being too weird.

So, I don't know, maybe you could "learn something" like that not everything other people do is about you.