I have an idea that I saw on a shirt on ebay once... it's not *entirely* panhellenic, but I thought it was cute
The front had a picture of a lion wearing a crown and on the back it said something like "..Because the REAL queens of the jungle wear the crowns" ... or something to that affect. I don't think anyone would take offense to it since it's all in good fun, but I guess it really depends on the campus atmosphere and if everyone else knows it is all in good fun
Hmmm... another Crush party tshirt idea could possibly be a bright orange shirt (or another color...) with the orange crush soda can on it.. and maybe you could write out ADPi Crush or something like that in the font that the soda can uses.