Slim, thin cardigans almost never look good buttoned up. They create this bulging around the hips that makes it look like you've got a deflating inner tube around your waist. I'm pretty fidgety in real life, so I do that all the time. I'm the same way. It feels weird to just let my hands rest by my sides so I'll often do what you're doing in that pic if I'm not holding something or have coat/sweater pockets to put my hands in.