Curses can be so much more than just “die motherfucker”.
That ignorant guy who always has an opinion but never looks up facts? Curse him to feel compelled to google every opinion he expresses, let it be an itch only temporarily scratched. That way he is both annoyed as fuck (and knowledge can be a real pain) but at the same time you make him more informed.
Of course, the curse does not need to have a, so to speak, nice outcome. That dude who made a sexual comment regarding your body? Make him unable to get a boner except for when he doesn’t want it.
And the guy who laughed at you? Curse him to drool whenever he falls asleep on public transport. Or to always have a booger when at important meetings.
The more creative, the better – usually the small things are what really annoy people. Backhanded blessings are a thing as well.