Its not unknown for pickpockets and muggers to operate around the Rambla area so keep valuables well hidden.I was even warned when using my camera in the market,my Dad always says 'try to look like a mugger and not a mugee'but then he's a scruffy bugger.
The Kabul House - I can't warn you enough. WEll its more outside in the square where the action takes place, but if you're anything like me when you \finally decided to return to the hostel, you can't really fight off a gang of theives. Ha. Actually I did try one night. Drunk old me did a karate chop at some poor unsuspecting guys who were pickpocketing a girl not 2 meters away from me and my friend. Hmm Silly stuff that. They could've killed me, but considering how stupid it was they must have figured I was a psycho or somthing and left. Anyways thats another one of those stories I should really learn from.
You must be aware with pickpockets (Most of them are Moroccoan people without documentation living illegally in Barcelona), particularly in Ramblas and some crowded metro stations.