try food coloring in the water. That's always fun. A crapload of
   green for st pattys day. Or blue just to freak people out.
   Yellow food coloring makes people think "oooh, buttery". (I
   don't do that so much anymore, but did it a LOT as a teenager -
   for some reason, I got kicked off spaphetti duty for a month or
   so) "