They have decided you are wrong and that what you’re saying is unimportant. At the same time, they’ve decided that they know better, that they have some kind of superior knowledge and already understand what you’re saying without giving your opinion or insight any kind of real attention. They are flippant, condescending, arrogant, cavalier. They are also opportunists. They’ve taken this opportunity, after you’ve expressed something that has meaning to you, to belittle what you are saying; so that they look bigger.
The attack could be passive-aggressive, a way to brush you off and imply that what you’re saying isn’t valid. Or they will impose their huge opinion over the top of what you say by saying it bigger and louder. Either way it is an attack. They want to make you feel bad and shut you down.
One reason could be that they are scared of what you are saying. They have to defeat it because it challenges one of their beliefs. What other reason for them to be competitive and cruel? They are afraid.
Another reason, which I already alluded to, is they just want to seem better, superior. This certainly goes along with their attitude and tactics; one of the characteristics of a dismissive person is that they are egotistical. They snidely and arrogantly purport to know the subject (whatever it happens to be) better than you. So, still, they feel challenged and must squash you and what you say. This indicates a good amount of insecurity and fear on their part.
What to do?
One thing you can do is question them. “Oh, really?” That’s how you can start it. Then ask them exact questions about the issue, to see if they really have it narrowed down. Nine times out of ten, they’ll be at a loss; because they really don’t know, they are pretending.
This is important to know too: It’s all pretense. Even their tactics exude pretense. Often they will be pretending to “help”. Of course, what they want to do really is shut you down.
The other thing you can do is plainly and directly tell them that they are being dismissive; that they are implying that what you are saying is unimportant and that they obviously have no regard for you. Some people, unaware that they are being rude, will suddenly see what they are doing and might even apologize.
Finally, if it is simply too tiring and a waste of time to respond to them at all, or they are relentless, you can totally avoid them and avoid talking to them; or at least keep contact with them to a minimum. Of course, this might not totally solve the problem of how they treat people but it is likely a wise action considering the perpetrator’s approach to life and how they treat you.
Simply put, you really can do without them.