Okay, so he knew it was vain. He knew it was probably stupidly narcissistic to so enjoy the sound of his own name, but how could he not, when Regulus said it like that? When it was sort of demanding and sort of entreating and followed by a breathless insistence that they were going to get caught. Not that he really worried over addressing it-- not when Regulus's body went a bit more taut, not when he could practically feel the undertow pulling at Regulus's so-called common sense.
And see? Just like that, Regulus realised he did know how to have a little fun. And maybe that was half the fun, the idea that nobody else every really got Regulus to do these sorts of things. Never really got him to do what he wanted to, even if he shouldn't.
A rumble of acknowledgement filled James's chest. Acknowledgement and something else, something that seemed to flare to life whenever Regulus could be compelled to say 'fuck.' It was remarkably similar to the spike in the core of his body that hitched up whenever Regulus grabbed at him.
"Yeah, but you wanted me to," he returned, perfectly certain of that, and managing to avoid jumbling the words together too much as he raked blunt nails down Regulus's side. One of his kneed angled itself between Regulus's thighs, aiming for a bit more pressure, a bit more friction. There was still Regulus's shirt to deal with, but he could get to that in a minute. James's hands came together to tease at the fastening of Regulus's trousers, fingers casually and intentionally stroking at him through the fabric. "And you want me to now, don't you?"
As if there were ever any question. But because Regulus was so fond of arguing for its own sake, James angled to cut him off at the pass by latching his mouth to Regulus's neck, his skin made salty by the sea air or the water itself, or both.