Stallion

Through the first four Rocky movies, Rocky and Apollo Creed go from not knowing each other and facing off in a heavyweight boxing match (Rocky), then having a rematch (Rocky 2), to teaming up so Rocky can avenge a loss to Clubber Lang (3) to again teaming up, leading to Apollo's unfortunate/it's a movie so obvious death in the ring (4).

So the two get to know each other and become friends and Apollo initially calls Rocky "Rock". 

Nothing wrong with that nickname.

But then things get awkward. 

Now, from the first movie Rocky's nickname was "The Italian Stallion", and that's fine. 

But beginning with the opening scene of No. 4, Apollo all of a sudden starts calling him "Stallion", and so becomes the first and, since his character dies about 8 scenes later, last person on the face of this fake earth to call him that.

Notable

(first four are just from the opening scene)

"Look, Stallion, when you won that last fight you beat me by one second..."

"Anything you say, Stallion"

"I'm still young enough to whip your butt, Stallion"

"You know Stallion, it's just too bad we gotta get old"

"Once you step out of that ring Stallion it's like you're ancient history"

"I don't really wanna hear this Stallion"

"No Stallion! Maybe you think you're changing!"

"I feel like I could eat nails, Stallion"

Again, because of his death in the ring to Ivan Drago, Apollo is only in the film for the first 33 minutes. But in that half hour says "Stallion" 20 times!

That's a stallion once every 1.6 minutes of movie.

Impressive.

** Next up on Goodness Gracious What Is Going On In Rocky 4: why no one seems concerned at all that Paulie's new (first?) girlfriend is a robot.