The word crazy qualifies a human being or an animal not behaving in a way that makes sense, acting differently from other people because of a mental trouble, and that behaviour can last or get back to normal. Crazy can also refer to someone stupid, idiot.
This word may have a gratifying meaning if it refers to a project, an idea or a situation which goes out of the ordinary. An ambitious project can be defined as crazy if it is impossible to achieve for example.
It may refer to an item that would start running in a weird way, such as a computer which would switch off by itself without any reason, or an escalator that would start going down instead of going up, like the case in Japan, in August 2008 making everyone fall.