It has come to my attention that as an Evil Overlord, you should not say, “Bless You.” You are evil, and you do not want to bless people. Instead you want to curse them in some way. Let them know that you feel nothing for them, and that you hope that their health worsens. After all, if they are ill, they will have a greater struggle to overthrow your empire.
Nor can you walk around saying, “Curse you!” People will just think that you are mad and angry, and maybe you want to kill them. I am not saying that you do not want to kill them, but you do not want to let them in on the fact.
Since the traditional way to bless someone is the German word, gesundheit, it would be best to use a German word to not bless someone. The opposite of healthy is diseased, and the German translation of disease is krankheit. Therefore, whenever someone sneezes, you should respond with the proper krankheit. Go on, give it a try. Say it outloud. Does that not feel good to say?
Update June 27, 2007 – Something I overheard recently, which I find very appropriate: Pestilence upon thee.