1. Creating an alter ego. This can be seen in musicians, actors, writers, et al, but can also be found in the guy on the corner telling you that he is either Superman, Jesus Christ, or a grilled cheese sandwich.
2. Growing a beard and not caring about your appearance. Again, either you have rejected society's standards or society has rejected yours.
3. Writing poetry. Writing poetry well makes you a genius. Writing poetry poorly makes you a lifeless ingenue.
4. People who commit suicide. If you kill yourself for art, you are a troubled genius who saw this life as the sham it was. If you kill yourself for a religion, girlfriend, or just happened to be experimenting with some weird choking fetish, you are crazy.
5. Being a politician. Either you are absolutely infatuated with humankind and its improvement or you are a megalomaniacal narcissist who will try to kill us all.
6. Speaking several languages. People who can speak and study in several languages are brilliant, but people who speak in several languages to no one in particular are crazy.
So far, this is it. First the good news: if you aren't one of these people, you aren't crazy. Bad news? If you aren't one of these people, you aren't a genius.