The Little Tony (Iron Man)
It's crazy that the physical pain of dissolving away into the ocean is secondary to how much it had hurt to see Steve and Bucky smiling at one another, curled in close and crushingly happy -- no space in between them for Tony. And Tony's not good or sentimental enough, even, to hold close the memories of Steve from when he'd been walking around on fucking glass just to walk around near Steve and his sunshine-bright smiles. He resents it, he regrets it, he's not the kind of person who's unselfish and grateful enough to be happy for Steve to have Bucky, who can live with him and care about him and be good to him like a normal person -- not like Tony at all.
And Tony's fully prepared to go pissed, to vanish into whatever's after angry as hell that he'd bartered himself away so cheaply, but then Steve's tumbling over the dunes, panic in his blue eyes, skidding down the length of the beach to where the waves are dragging Tony away, piece by piece.
"Tony," Steve gasps, and he puts his huge hands -- gritty with sand -- on Tony's face, and presses their mouths together: fierce and bright, a sudden electrical pop of sensation. "Tony -- thank you, for everything."
"Oh," Tony says, "God damn it," and he can feel himself disappearing faster now, smiling crazily, something bubbling up like happiness in the spaces where he used to be, all the anger melting away.
"Goodbye," Steve tells him, wet-eyed and still perched close, watchful and intimate. "I'm so glad I knew you."
"I don't care that you're getting married, Rogers," Tony tells him, with his literal, last breaths. "You still owe me a date."
Steve laughing, crying, eyes wet and huge, saying, "Yes, of course, anytime," is Tony's last image, framed in the light of the sunset, and Tony is filled with a sudden surge of determined inevitability, because he's coming back, somehow the ocean is going to give him up again. There's no way he's not cashing this in eventually.