maybe you can call them and tell them they have won a contest of some sort, or that their name was drawn at random, and they must go pick up the prize that day, or lose it... then when you see them leave...get the cat! LOL just kidding but it would be funny, and if they are as mean as you say, then ha ha on them !!
LOL hey it's 1:30 AM here, it's all I could think of!