And Ne-Yo admits he was baffled by the actor's behaviour.
He tells ET Online, "I didn't understand the concept of staying in character the whole time. We almost got in a little tussle just behind me not understanding that he's still in character... (Eckhart) plays a tough guy in the film, so it was lunch and I go, 'Hey, Aaron.' And he goes, 'Leave me alone.'"
But Ne-Yo insists working with Eckhart was an eye-opening experience, adding, "He's a fantastic actor. I learned a lot just by watching him."