Attempts to deny the rationality of one's opponents numbers among the greatest affronts to rationality.
Rationality, after all, is the process of clearly defining and stating reasons for one's actions or beliefs.
By the nature of life, people will often find themselves caught in situations dominated by low quality discourse. Failure to match the style of the day means one's ideas go unheard.
It may not always be possible to engage in high quality reasoning. However, once a person takes the path of actively denying their opponent's rationality, that person becomes part of the problem.