Edgar has a habit of telling jokes during meetings. others laugh, but it really does slow down the meetings. josh, edgar's manager, has asked other meeting members to refrain from laughing when edgar tells a joke in future meetings. josh is hoping edgar will stop wasting time with the jokes. jonh is using extinction to change edgar's behavior.

It is true that John is using extinction to change Edgar's behavior.
He is making his behavior of constantly telling jokes 'extinct' by letting his colleagues know that they shouldn't encourage him to continue behaving the way he is behaving. Thus, eventually, given that he is no longer 'rewarded' with his colleagues' laughter, he will completely change his behavior and stop joking around when it's not appropriate.