This is a great question and maybe a little difficult to answer. This is my opinion: for the people who do the work in a bank, the managers, the tellers, the customer service representatives and so on, I think they should answer the 'what do you do?' question with exactly what they do. They should say 'I'm a bank manager', or 'I'm a bank teller' or simply 'I work in a bank'. To me (and especially in recent times with all the bad press the banks are getting), 'a banker' is someone in a high position or who owns a bank. With the recent news in Cyprus, people are saying 'the bankers' are stealing citizens' money. They are referring to the high level bankers, not the ordinary workers in the banks.