No. Calling someone crazy is considered rhetorical hyperbole - it is not meant to be taken as a diagnosis of a mental illness and most people would not take it to mean someone was mentally ill. If, however, you had your character say that someone was a sociopath or psychopath, then that
could be taken as slanderous, depending on the context in which this was said, because those are actual mental disorders.
Calling someone crazy is like calling someone an idiot or a fool or weird or strange - just opinion and/or hyperbole and perfectly legal, although not very nice.
(in addition, if your character is referring to a Hollywood celebrity, chances are "crazy" would also be the truth - which is a defense to defamation
)