I don't put an entire woman into my pocket.

Fair, average thickness is somewhat meaningful when you have other stuff in your pocket. However, all phones are thin enough these days it’s kind of a silly comparison. Linguistically it’s a more interesting question IMO than in terms of marketing nonsense.

I think for people thin is mostly in reference to volume for a given height. But there’s a bunch of related factors involved like weight and clothing sizes which keeps it relatively ambiguous.