This is an interesting one! I am answering based on the majority of customers who I feel will find it rude on the part of the cafe to charge customers more who they deem to be rude. Who decides what constitutes rude? I think some people will actually like the idea though. It may bring out better behavior in some.
I'm often surprised by how rude customers can be in restaurants and stores. It's as if they are given a free pass to belittle or demand that they are treated with more preference. The idea of a cafe charging rude customers more is a great idea and would require customers to apply common politeness when interacting with staff and other patrons.
The idea of seeing rude, loud-mouthed people getting some kind of punishment will appeal to those customers who prefer to drink their coffee in civilized company. The world is a far better place when people are pleasant and polite, so as long as the staff at the cafe are equally polite, there is no reason to think customers will be turned off by this concept.
The problem with this concept is that everyone has a different opinion as to what is considered rude. If a set procedure cannot be followed then it may lead to someone who wasn't intending to be rude being charged more. It may appeal to some but I feel that many would see it as a hurdle and not bother going to that café.