revenge without causing harm? kind of redundant. i would look for a revenge hex and while casting specify either in a chant, or through visualization, what you want to happen. a bad luck hex could also help. i believe it's been posted on the site, but try the 'you messed with a witch' chant.
with all these options the person will receive some type of ill effects. most likely no bodily harm, but they might fail a test, loose their wallet, their favourite shirt destroyed in the wash. little things like that. if it's justified you shouldn't feel any negative karma from the hex.