People on the Barcelona metro aren't so rushed... it's not like they have jobs to get to.
Srsly - Barcelona's metro is nice - but a girl who was traveling with us almost got robbed. She was sitting with a big purse in her lap that was open-topped. A few seconds before the train pulled of the metro station - a guy bolted through the traincar and tried to scoop her wallet out of her purse and make it out the door just before it closed so no one could go after him. He made it out the door and the trained pulled off before anyone could react, but he didn't manage to grab anything because he scooped his hand in mid-stride.
The advice our guide gave us is if you are carrying anything like a messenger bag is always position it in front of you, not behind, and if there is a flap (which is ideal) wear it with the flap facing INWARDS to make it hard for the pickpockets.
Also - if you are at a metro paystation in downtown Barcelona and you find the credit card reader doesn't work because a coin is permanently jammed in it - sorry - it was a really