I've always felt safe in Bangkok, and Thailand in general. I lived in Buenos Aires once about 10 years ago, and back then there was loads of theft. It was one of the first things my landlady warned me about when I arrived. In Bangkok I leave my laptop on the table in outdoor coffee shops/bars etc when I go for a slash but if you did that in BA, your stuff would be gone by the time you came back. They wiz by on scooters and snatch it. It's a pity because it's a very beautiful city.