I am translating your post into 'you have a younger brother or siser who did you wrong and you want advice on seeking revenge'? If so....
If you are the passive aggressive type, you could just clean out the toilet with their toothbrush and chuckle everytime you see him/her use it... OR
if you are the confrontational type...you could just corner them and have it out for once nd all...or you could pass a rumor about them amongst their friends...like that they wet the bed or something... OR
if you are mature, you could just let it go and move on... life is too short for petty differences...
I think #3 is the best route to go.
