Disclaimer: I do not own TVD.
Since the near run in with Elena not long ago, Death decided it was time to start properly using his powers again; he was getting rusty with them and that wasn't good. He couldn't allow Elena to die, he needed her to remain alive, at least till his son took over, but she was making that incredibly difficult.
She'd come close to dying again, with the hunter, but Death made him miss. A little pressure on the arm, and bam! Elena was still alive; Hallelujah! But then there was the curse, blah blah blah, he didn't really care; he didn't even have to do anything here. The Salvatores did all the work for him really.
Then she had to go and kill Kol. Don't get him wrong, he enjoyed adding another Original to his collection, but now there was a one hundred and ten percent chance that she was going to die. Fuck it all. Using his powers of manipulation, he managed to get the Mikaelson siblings to forget about revenge on her, even managed to get Rebekah to become her friend (He knew he was good; he just didn't know he was that good).
But now he found himself in a dilemma just as bad, somebody else he truly couldn't stand was likely to die very soon. Hayley fucking no-last-name. He knew she was trouble when he first noticed her, at the Lockwood manor, but boy did he not know how annoying she was.
Hanging off that Lockwood boy, continuously flirting with him, literally having no depth as a person (Seriously, did whoever make her just forget to give her a personality?).
He didn't think she would actually be stupid enough to do anything to warrant her death, but then the Hybrid fiasco came about, and that meant there was a mark on her head. That night was the first time he relapsed and ate an entire tub of Ben & Jerry's; it seriously helped the emotional pain.
Now, as she stood facing Klaus, who he knew was likely to rip her heart out any second, he knew what he had to do; desperate times call for desperate measures.
Summoning up all the lust he could manage as quick as he could, he shot it at Klaus, and next thing you know, extremely awkward Hybrid-Werewolf sex. Crisis averted; Hayley and Elena should not be joining him for a while.
As he stared at the horrifying image in front of him (He may have made it happen; didn't mean he liked it), he realized that preventing annoying teenage girls from dying was much more hassle then it was worth; perhaps it was time to retire early after all.