I find it to be one of those words that has a very ambiguous meaning (much like the word "normal"). Everyone has their own definition of the word, but we use the same name to describe its value and concepts.
I could quote the dictionary that it describes one to be mentally deranged, manifesting in wild or aggressive actions. That's too simple really. I've heard that it's a good sign to ask yourself if you are crazy, as doing so means that you aren't. It's too easy to say. The mind, however, is anything but simple and easy. Despite what we may tell ourselves many times, we must realize that others such as ourselves are just as complex as anybody else. Rather... that have the potential to be so.
In that complexity there's a myriad of variables, leaving it to be anything but possible to identify each and every one, let alone flawlessly understand them. Does fact that we are all forever in a constant struggle to fully understand ourselves, that it means something different to everyone, make us all, to a certain extent, "crazy"?
What does "crazy" mean to you?