The Vita is too bulky to carry around anyway unless you are wearing baggy gangster pants with oversized pockets normally used for carrying a gun
Holding a portable console without a case in your trouser pocket is silly and causes more damage than it's worth - enjoy pulling all the lint out of nooks and crannies. PSVita Master Race uses console cases. That being said, my PSVita fits my hoodie pocket just fine, I've never had problems with it in terms of portability.