Whos right and whos wrong (work situation)?

You were right, it sounds like the signs indicating the policy were clearly posted. He had a right to be upset but he didn't have the right to try and bully and threaten you about losing your job for trying to enforce the hotel's policy. If he's a friend of the manager, ask the manager to come to the desk and explain the fee. If you are fired, contact a lawyer for unlawful termination, you should not be fired over enforcing hotel policy.