Any suggestions?

My son is normally a very sweet, loving boy and now that he turned three we have definitely seen a drop off in the tantrum department (thank goodness!). The only problem we are having with him right now is with the phrase "shut up." When I tell him to do something he doesn't agree with, he says, "No, shut up." I have tried everything to get him to stop doing this and it seemed to get better for a couple of months, but now he is doing it again full force and worse than ever.

I have put him in "time-out" in the corner as well as in his room. He yells out from his room "shut up, shut up, shut up." I have tried simply ignoring him which seems to work for the time being, but he will still say it again the next time he doesn't get his way. I have tried washing his mouth out with soap. He did hate the taste and I thought it would work, but he said it again later that day.

I will ask the pre-school teacher tomorrow when I go in to substitute if she has any suggestions, and I would love to hear any from my readers as well. At this point, we will try anything, so give me your craziest ideas - I want to hear them all. Thanks!