The veteran actor admits he used to get "jealous" if one of the other action heroes - who appear in his new movie 'The Expendables' - landed bigger or better movie roles than him, but claims their rivalry made them better in their careers.
He said: "I was very competitive with them, and very jealous if they got a better movie or script than me. That's what made us push so hard. That's what made us push so hard, and it's why Arnold was so great.
"He was far more diligent than me; I was too reckless. He's very machine-like and I did consider him an enemy. But, looking back, it was a good enemy."
The actor and director - who starred in both the 'Rocky' and Rambo' franchises in the '80s and early '90s - admitted he was "shocked" by Bruce's ad-libbing in the final scene of 'The Expendables', which pays tribute to the blockbuster action films of the era.
He added to FHM magazine: "I had written Bruce and Arnold into the movie in two different scenes but, to give Bruce credit, he said, 'Why not put us in the same room'. If you're going to get away from 'Rambo', you have to have that touch of humour in there, but still I was shocked by Bruce's ad-lib.
"He goes, 'Why don't you just suck each other's c**ks?' I thought, 'You can't tell Rambo and The Terminator to suck each other's c**ks!' I said to the guys, 'You know what, that's worth the price of admission alone!'"