4. Gary Busey
The guy has a face that tells you everything you need to know about his mental state - seriously, how does he even pull that expression? Busey is known for his insane ramblings in interviews, even famously chewing out a young teenage girl who was asking him some harmless questions once. Some suggest that his eccentric demeanour stems from a 1988 motorcycle accident in which Busey was not wearing a helmet and suffered severe brain damage, a theory corroborated by one of his psychologists. In addition to this, Busey has overdosed on cocaine, been questioned for assaulting an air hostess, charged with spousal abuse, been sued for refusing to pay his rent, and has now had to file for bankruptcy. Though that last one isn't the indication of a madman, the guy's troubled personal life is clear, and tends to bleed into his film work; after all, why else would anyone star in Piranha 3DD lest they were brain damaged?