How to be Insulting in Banks: Take a tape recorder with you to the meeting with the manager. Say nothing the entire time, but simply record all he says to you. Then when he's finished play it back to him at twice the speed and leave.
How to be Insulting on the Beach: Try to find seaweed and drag this along the beach, leaving bits beside other people's places.
How to be Insulting in Church: Pour water into the font and wash your hands in it. If you're really daring, take off your shoes and socks and cool your feet.
How to be Insulting in Banks: When ordering travelers checks, try to get the smallest denomination available, and then take ages signing each check in front of the cashier.
How to be Insulting in Church: If you just want to look inside the church, go in when you see the sign 'Service in Progress'. Take photographs with a bright flash-gun.