We all know someone who scoffs at the idea of anything out of the ordinary. They immediately shut down any uncommon or unproven thought as ludicrous or preposterous. Basically, they refuse to let anyone enjoy something they don't observe or believe in themselves.
This school of thought is annoying and boring. And if this is you, please just stop.
You really don't have to make someone feel inferior because they choose to open their minds to something yours cannot comprehend. Even if you think they are spouting absolute nonsense, it really harms you in no way.
In fact, asking questions and generally inquiring to know more about something you find absurd is a much more positive and constructive way to go about a conversation of this kind. You allow the other person to feel important while gaining another's viewpoint.
You truly gain nothing in life by looking through your own tunnel vision and shutting down any conversation you don't understand. Rather than making fun or poking holes, try considering another perspective and giving the idea more than two seconds of conscious thought.
This philosophy goes for any uncommon viewpoint, whether it be about religion, conspiracies, supernatural ideologies, etc. There is plenty that we don't know about the world, and blocking out anything you don't agree with will not allow you to grow as a person. Believe it or don't, as long as you take the time to listen and understand.
The world has enough boring and mean people. If you can't allow yourself to be open to something new like astrology, at least make people feel good by listening with a genuine desire to understand. It really doesn't matter if you believe in astrology, or anything for that matter, just don't be a dick and let people enjoy things.