Or they will use every fancy word that they know one right after another so that you will think that anyone that smart must be right and agree with them.
When someone tries a proof by intimidation on you, be calm, ask questions, and remember: you are not stupid, you can follow an argument that is presented carefully and clearly, and it is their job to help you understand. If you don't understand their reasoning, their statementt hasn't been proved.
Similarly, when you are absolutely sure that your reasoning is sound, but the person you are explaining it to cannot understand it, don't resort to proof by intimidation! Remember that it takes two people to communicate, and it is not always easy to do. The best thing is for both of you to relax, listen to one another and ask questions. Sometimes the very best thing is for the person who is trying to understand to explain what they know slowly and carefully while you bite your tongue and try not to interrupt. Then, when they ask you questions, you can answer them. Or maybe, just by having a chance to think about it slowly, they will come to understand what you were talking about in the first place.