Google "Reversing Spell." Those spells return the yuck right back to the person who sends it out. In my opinion this family of spells is a little "kinder" than an all-out curse, which no matter how you word it, a karma-sender is a type of curse. They nake nice ones using a box of mirrors, but there are other reversing spells that aren't as arduous to construct.
(And just for the record, i don't have a problem with justified curses.)