Barcelona is damn bad for pickpocketing so watch yourself if you are in town and look around you for potential thieves. Be especially vary of people who are very nicely dresses as it's a normal rouse to dress sharply so you have your guard down. Also a jacket casually over the arm can be a sign that they are looking for quick dives into open handbags etc. I usually just assume an agressive posture and look around. If you don't look like an easy mark or more like someone who could potentially fight back they will target someone else.
Being Spanish and living here for the last 3 years I have never been pickpocketed or robbed but know a lot of people that it has happened to and especially people visiting.
So if you come to Barcelona, always walk with your wallet in the front pocket, carry a bag in front of you on escalators or on the metro and if you are, two keep an eye on each others back and you won't have to run to the consulate for a new passport and deal with canceling all your cards.