The Sabbath guitarist revealed that Osbourne cut a dead shark apart and drenched the room with its blood as he got bored of taking drugs.
Iommi told the New York Post: "With drugs always you get bored, so you must do something to one another.
"Like Ozzy hauling a shark through a window, dismembering it and soaking our room in blood."
Talking about his friendship with the frontman, Iommi explained: "I talk to Ozzy couple times a week. He's up, down. I love him, although his attention span lasts three seconds."
The four original members of Black Sabbath - Osbourne, Iommi, Geezer Butler and Bill Ward - are due to hold a press conference in Los Angeles on November 11 at 11.11am (PST) / 7.11pm (GMT).
The event will be held at Whisky A Go-Go, which is the same venue where the band made their LA debut on November 11, 1970 (exactly 41 years previous).
It is rumoured Black Sabbath will announce their reunion and the prospect of recording new material together.
> Ozzy Osbourne: 'Black Sabbath reunion a strong possibility'
Listen to Black Sabbath's hit 'Changes' below: