Al Pacino finally admits his 'Heat' character was high on cocaine throughout the film.

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This explains a lot.

"GREAT ASS! You got your head all the way up it"

According to IMDB:

In an early draft of the script, Vincent Hanna had a cocaine habit, which, according to Al Pacino, explains his bombastic outbursts.

So while that's Pacino's interpretation of the character, he did Portray the character according to Mann's initial belief. Eventually the writer-director decided against this plot point, but it was, clearly, still in the back of Pacino's mind when he decided to tackle the character on-screen.

Pacino explained that the character is supposed to be strung out on cocaine throughout the film at a special Academy screening of "Heat" in L.A.

“I don’t think I’ve ever said it out loud,” Pacino said, explaining with words what his actions had already clearly stated. “But I’ve always wanted to say it, just so you know where some of the behavior comes from.” Next thing you know, he’ll be telling us that Tony Montana was a coke head, too.