First, the bank might not care whether it's really you. If there is someone with "bad behavior signs" who is sufficiently similar to you the prudent thing to do if you want to minimize loan risk is to assume that it's you. Secondly, it's really simple to deanonymize data. Check for example

http://33bits.org/2011/03/09/link-prediction-by-de-anonymiza...

As the site name implies, you need just 33 bits of good information to distinguish every person on Earth. It's not hard to get enough bits from your Facebook timeline to cross-correlate it with other stuff the bank might know about you.