What does it mean?
you're over them too.
THE CONTEXT:
Brussels sprouts are great, but hipsters, you have turned them from a cool vegetable to an unstoppable, inescapable craze. Now they're so trendy we bet you're over them too.

Question

Answer

being "over" something simply means you are no longer concerned with it. let's say you break up, if you are "over" your ex girlfriend it means you no longer have feelings for her. So, this would mean they are no longer "crazy" about brussel sprouts.