Answer: he used informal langauge, slang .public speaking is formal and the used of slang or informal langauge is inappropriate.
Explanation: Informal language can only be used amongst peers but when it comes to public speaking a formal langauge has to be used .
It start from greeting people one can not casually do so as he did when he said whar up; that is a language that he can only use when it id just him and his friends .