Lord knows, a hostile person can dredge up enough ammunition by themselves, without your providing the shells to load into the weapon. You can be sure that if you sigh, rollyour eyes, show frustration, mutter, or do similar things, that you are reloading the person’s weapons.
Your words and actions can also be used against you if the customer chooses to lodge a complaint with someone else in the organization. For example, when you slam the phone down noisily on an obnoxious customer, what you have done is to encourage the person to complain to someone, and claim that you slammed the phone down, or you were rude. And then you have to explain, and get more frustrated with the situation. You don’t need the hassle.
Things that you say can also be used as ammunition against you and your company. Be aware that some hostile people will try to get you to agree to something, so they can use that agreement as a weapon when talking to another staff member. For example, a person complains to you that Jim, a colleague of yours, gave him the wrong information. Without looking into it you reply “Well, obviously Jim was mistaken”. Your customer may very well go back to Jim and quote you or say something like “Even [your name] thinks you’re wrong, your very own staff’. See the problem? So, one thing you want to think about is what kinds of things you say and do that might be used in the attack on you, or on another person.