What was there to negotiate with a man who was repeatedly telling people he planned to start WW2, and that all attempts to negotiate with him would be used and abused to benefit his campaign of recreating a German empire? A man who would go on to make a deal with the Soviets against western nations, agreeing to divide Europe in half with Joseph Stalin?
Er, and this all does not apply to Putin?
Herr Hitler was all reasonable in May-June 1940. He fooled some people at the time (Lord Halifax for one, who almost became PM during that crisis).