When in the public vicinity of your target, be inconspicuous and:
Look towards them and cut/break a hair tie (or rubber band) to make it hard for them to hold something back in public (ex: their true self, or if you want to be literal, their hair on a humid day)
Lay your hands on a table or similar surface and channel all the things you want to express into a pipeline of energy. Send it to them and cut the pipeline off immediately.
Tap out your intention in Morse code (ex: say "hex ex" over and over again with energy and intent behind each tap)
If they carry a bag, create a "magnetic" force of energy to attract bad luck to the bearer and visualize it attaching itself to the bag.
To weaken their immune system, get a tissue and write their name onto it. Fold it in a way that reflects the opposite creases it was pulled out with. Make it as small as possible. Blow your nose into it if that isn't too strange for you. It will send off your sickness or negative energy as well, so it's a win-win.
Break an old pencil to shatter their stability. Throw it away in the public trashcan nearest to them.
Spell their name in dirt, dirty snow, gravel, or road grit. Leave it in a high traffic area to get pounded into the ground.
Devise a simple but unique gesture to use as a way to trigger a curse. When their back is facing you, discretely make it and direct energy towards them. Keep this gesture a secret.
Put a very small amount of lotion and sand in a container. Mix it well, and slather over an image of your target. This is to have them wounded after doing or receiving something they expected to be pleasant.
If you live in the home of your target:
Switch their cereal box around as well as any other things they often eat. Moving them is good enough, but adding intent could turn their whole day into a tizzy. Do not meddle with the food contents!!!!
Put an energetic sigil on their door to bring the occupant bad luck. Ward yourself accordingly.
If you compost, bury them to become useful fuel via lovely worms by shaping a poppet of them out of veggies and other organic materials. It would be wise to use foods that they enjoy and/or ate other pieces of, but a general poppet with the right intent will do its job just as well.
Draw a map of your home and highlight their bedroom. Ward your home well, but leave this space completely open. Remove protective energy from there to leave them vulnerable.
If you don't see your target on a daily or regular basis:
Write your target's full name (and any identifying info) on your garbage bin (or write their name and info onto paper, spit on it, and throw it in).
Flip a well wishes card inside out and black out the positive words. Add your own, mark it with their name, info, and/or photo, and then seal it in an envelope for safe "delivery". Throw this away.