When defusing, one should use choice speech congruous to the situation. You need to also have a solid understanding of the type of person you are dealing with on a behavioural level in order to 'speak his language' per say... it's important the potential threat/bad guy can relate to your words therefore choice dialogue becomes extremely important. You need to control the situation on a psychological level-using psychological warfare. This is where most fail to understand the power of communication.
Sixty percent of communication is body language; thirty percent is tone of voice and ten percent of communication are the actual words spoken. Based on this, the visual cue you are giving your attacker can telegraph your intentions.
This can challenge his ego and insecurities forcing him to become more aggressive and violent, threatening him, raising his guard and preparing him for a fight all of which are things that do not strategically serve you during a potential fight.
Be careful what you communicate to your opponent. Therefore, your body language should conceal your true intentions to maximize your safety and allow implementing a strategy of your choosing at the time of your choosing.
By talking, you take control of the situation instead of letting the situation dictate what you should do. It will create a sense of over confidence and draw him closer to you, without elevating the level of violence,
even if it dos, his action will be highly telegraphed so that is will trigger your reflexive response
(Attack around the centreline: Taan Dar concept - Attack through the centreline: Fook/Wu concept).