The term crazy people is one we use interchangeably. We use it when we are talking about people who are just naturally funny in the things they do and say, without even trying. They are usually referred to as the life of the party because you know you are going to have a good time if they are around. We also use the term crazy people when we are speaking of or about those who have some sort of mental disorder in one form or another.
For instance, if you have ever known or had a conversation with a person that suffers with bipolar disorder while they are in the middle of one of their episodes, your response may be "I do not deal with crazy people". The reason for this is the person suffering with bipolar goes from one extreme to the next. So this person that you may have communicated with for some time now will all of a sudden one day just flip the script on you, and if you are not aware of what is going on with this person, this will cause you to say this person must be crazy.
The same is true of dealing with people who have personality disorders, they may also be lumped into the crazy people category. Stresses, sudden changes or just simply not agreeing with the person 100% may cause a person with certain personality disorders to become someone you do not know. Because you are so caught off guard when this happens, again you will choose not to deal with crazy people. People with a personality disorder or not necessarily crazy people, but because of how they react in certain circumstances can seem that way to those who are being abused by them at the moment.