Tony hated the implication there that he didn't have a heart, that he didn't care at all about her or anyone else but himself. Pepper had done what she'd meant to do as he felt her cold stare on the back of his neck enough that her words and gaze raised the hackles on his head. His fists clenched at his sides and she could visibly see the lines of muscle tighten along his arms.
"How dare you say that to me!" that small bit of anger bubbling just below his surface now pouring out. "Everyone wants something from me, constantly asking me to do things that I don't know I can do. What is it that you want from me, Pepper? Huh? I go out there," his arm swinging out to the side to point towards the ceiling, "and save people, killing men that would otherwise massacre a thousand if I left them alive to lick their wounds another day. I put that goddamn suit on and blow up weapons, my weapons, that are being used to harm innocents, and you stand there angry at me for falling short of the perfect image of me you've created in your head. I do all of this and I am not supposed to have a heart?"
Tony seriously hadn't realized he'd been doing it during the entire tirade, but he'd gained ground and come toward Pepper in a manner that spoke he might strike her if he were within the distance. "I am not perfect. I never will be. What is it that you want! Do you want me to come home after every fucking mission where I'm bruised and bloodied and can barely keep my eyes open because I haven't slept in days and just play the perfect boyfriend? I'm tired of falling short of everyone's expectations and getting pissed on because I do."