Steve peers over the top of his book when the paper aeroplane is lobbed at him.
"Stark, I'm reading."
"Yup. Finally catching up to the modern age," he smirks. "Careful, though. Everything goes to hell in the fifth one."
"Hey! Don't tell me," Steve says, annoyed.
"Ah yes, spoilers etc." Tony shrugs and looks thoughtfully at the book, before grinning. "Okay, I'll honour the code; not a word from me."
(And when he's finished, when Stark throws him a surprise birthday party, Steve wonders whether the lounge is decked out as the Gryffindor common room for his sake, or Tony's.)