To be "dismissive of" something or someone means to treat it/them with a lack of seriousness, respect, or consideration, often displaying an attitude of disregard or indifference.
It involves ignoring or minimizing the importance or validity of the subject in question.
Here are a few more examples to illustrate the usage: "She was dismissive of his achievements, believing they were not significant."
"The teacher was dismissive of the student's questions, implying they were unimportant."
"Some critics are dismissive of the new technology, claiming it won't have any real impact."
"He was dismissive of her concerns, thinking they were unwarranted."
In these instances, being "dismissive of" something or someone reflects an attitude of not taking it seriously or showing little consideration or respect, often to the detriment of productive communication or understanding.