A smout is a "smiling pout" popularised by celebrities such as Kate Bosworth and Renee Zellweger. It is a closed mouth smile with a small pout which perfectly complements the skinny arm pose when being photographed on the red carpet.
Girl 1: Babe you look soooo damned hot in that photo.
Girl 2:It's cos I'm smouting and doing skinny arm babe. It just helps you work it in photos.
Girl 3:I am totally gonna give up smiling and start smouting.