I had a parent threaten to sue me once because a "grill" went missing that was actually a piece of foil. District had a policy that said no grills. Parent claimed it was worth several hundred dollars. Principal said I would have to pay based on what the parents claimed it was worth. I have a friend who is also my personal attorney. He said to tell the principal that I needed proof of purchase and the value of the missing item. Once I told the principal "my attorney has asked for the following information" the matter died.
Stand up when you need to and more importantly, don't pick fights for no reason or look for trouble when it isn't necessary. Walk lightly and carry a big stick.