This is pretty silly. Hope you like it! (I'm still taking prompts, btw. Don't be shy.)
Clark has spent a fair amount of time mourning for Lex. First he mourned their friendship, then he mourned for the man Clark had hoped Lex would become but didn't.
Then when Lex died he mourned for the man he was. Because even an evil Lex was better than a dead Lex, and no matter how bad things had gotten, how horribly things had ended between them, Clark missed Lex more than he ever thought possible.
He'd have given his right arm to hear that cool, silky voice one more time, saying his name, talking about some long-dead bloodthirsty tyrant that Lex inexplicably admired.
Which is why when he heard Lex's voice saying his name that Tuesday evening, in a split second Clark had the imposter held up high against the door to his apartment, hand around his throat.
The real Lex Luthor, back from the dead. Again.
"Huh?" Clark lets him go and Lex clutches his neck, coughing. "How?"
"It's me, Clark. I'm alive. That you actually thought I'd let myself get killed by that Robin Hood wannabe is extremely insulting by the way, but thanks for caring. It meant a lot."
Clark takes it back. He'll keep his right arm, Lex can shut up, and maybe he'll call Ollie to make sure he does the job properly this time.
"It's been a while. You look great." Eyeing him up and down, slowly, seductively.
"What do you want, Lex?"
"To rule the world. But before I go do that I thought I'd come visit my old buddy, Clark Kent, say hi, see how he's doing."
"That's good. And how's Superman?"
Oh crap. It'd been so many years since Clark last saw Lex he'd forgotten Lex knew his secret. "He's...fine."
"I won't tell anyone," Lex says with an easy smile.
Clark grits his teeth and eventually says, "Thanks."
"On one condition."
Lex's eyelids droop and his gaze travels down Clark's torso, lingering on his groin before travelling upwards again, until he's smiling sleazily into Clark's eyes.
"What?" Clark asks again slowly, although he's not sure he wants to hear the answer.
The smile disappears and the expression on Lex's face darkens. "We're enemies, Clark. I'm about to become your -- sorry, Superman's -- most deadly nemesis. But before I go do that, I want to show you how much I care."
He cannot be serious. "Lex, you're crazy."
"That may be so. But I'm not asking for much, and what I am asking for I'm sure you'll enjoy."
Clark just stares at him, and waits for an explanation, but Lex doesn't answer. He just drops to his knees and looks up.
"You have got to be kidding me," Clark says, eyes wide with disbelief.
But Lex clearly isn't kidding because he's got one hand grasping Clark's hip, fingers of the other hand popping open the button of Clark's jeans, pulling down his fly. Clark's cock is in Lex's hand before Clark even has a chance to think of a reason to put a stop to this.
"Stop," he says halfheartedly, because he's getting hard and Lex has him in his mouth now, and Lex's mouth is warm and wet and ohgodsogood.
He doesn't ask Lex to stop again. He lets Lex suck on him, he strokes Lex's smooth head, he suggests they move to the bedroom. He takes his clothes off, he kisses Lex passionately, he fucks him for hours.
They say goodbye to each other in the morning, amiably, and Clark smiles at the back of Lex's head as he walks away. Perhaps having an arch nemesis won't be so bad after all.