I’m writing a realistic fiction story for a little writing practice (it’s just a generic (aka cliche) high school setting), so of course there’s the popular girls, who just invited a new girl into their posse. They tell her that if she tries to ditch them, they’ll ruin her life, but that doesn’t really sound too threatening. It just sounds cliche. I know this is a weird question that’s kind of hard to answer, but I’ll take anything if it means making my story slightly less cliche. 
‘I’ll destroy you.’
I’ll make your life a living hell.
“After all, there will be consequences. And I’ll make you pay for them.”
Depends, what sort of language is appropriate for this particular story? Because I know if it was me, I would say something like “I’ll f*** your life up” or “I’ll make a sh**storm of your life”. Maybe just go with jayden101’s response…
“happy” will be so gone that google can’t find it.
That’s clever haha