Anywhere, really.

I lived in South London for much of my adult life, and became used to avoiding opportunist theft - things like putting a chair leg (or your leg) through a bag strap, always closing and putting away your wallet/phone/whatever before leaving a shop/taxi/pub, not carrying a laptop or camera in an obvious laptop or camera bag when walking around late at night, etc, etc - these all became second nature.

Now I live out in a small town, and my wife finds it bizarre that I would do any of these things. Or, for example, worry about leaving washing on the line when I leave the house.

I also find it odd to see all the warnings about Paris, and the metro. I used to live nearby, and have been visiting regularly (3+ times a year) for the last 25 years, and have yet to witness it.

Barcelona, however...