I have heard first hand story's of 9/11 celebrations that happend in Stockton Ca from a friend who live across from people that were Celebrating!
I have also heard other story's of it, So I go to snope's to see what they have to say.
And What do you know Snope's say's "UNDETERMINED" Here is a link
http://www.snopes.com/rumors/photos/shirt.asp
Then you can Google it Lots of story's and news about the Issue. Even You Tube.
http://www.youtube.com/watch?v=KrM0dAFsZ8k
But Snope's cant seem to come up with the fact's
Does this Shirt Exist ???? and Who cares if it does or not. Does the "Religion of Peace" celebrate 9/11 HELL YES.