This self breaking Karma spell enhances karma that will break itself.
I don't usually agree with doing spells on others, especially if it, at all, infringes on their Free Will, but this spell only serves a basic purpose of letting another become aware of their negative activities, in respect to how they affect themselves and others around them.
This spell does not set out to harm or demean anyone, nor mete out any punishment.  It just serves as a reminder to the individual that there will be karmic payback for their negative actions.

Once the person in question has stopped acting and feeling hateful, the spell will break itself:

Light a white candle and cocentrate on the person this spell is meant to help.  Say these words out loud :-

Listen to this spell I weave, take heed in what is told,
For your hatred and unkind deeds will return to thee threefold.
By the rise of the next full moon a witch will sit and weep,
For all the sorrow ye have sewn, thee will begin to reap.
It's not too late to change your ways and break this painful spell,
Replace the hatred in your heart so only love will dwell.
So mote it be.

Do not blow out the candle, but allow it to burn out.  Votive candles are safer for this use.
I have used this spell on people whose aim it is to hurt themselves, me and others around them.  It has worked, as the ones involved have come to me with realisations of their own and have, in some way, changed for the good of themselves and others.
Take care with your own feelings too.  Do not allow anger and agression to be part of the spell.  It must be said with great meaning and compassion.