I've been feeding some crows and now they are being dicks. Help

There is a murder that hangs out in a carpark I walk through on my way to work. For the last few weeks I've been giving them peanuts. Today as I was leaving the carpark 3 of them bopped me on the head as if to say 'giz more nuts bitch'

I enjoy feeding them but I don't want to encourage this behaviour! What do I do?