Comment Reposted to your Profile Page.
From the FAQ at blacksabbath.com:
"Ozzy said that Geezer was rhyming radio rental with mental so they started using the phrase radio when meaning mental. Radio rental rhymes with mental. Hence 'Am I Going Insane (radio)' means 'Am I Going Insane (mental)'."
(http://www.black-sabbath.com/faq/faq11.htm#faq11005)
From the FAQ at blacksabbath.com:
"Ozzy said that Geezer was rhyming radio rental with mental so they started using the phrase radio when meaning mental. Radio rental rhymes with mental. Hence 'Am I Going Insane (radio)' means 'Am I Going Insane (mental)'."
(http://www.black-sabbath.com/faq/faq11.htm#faq11005)