They will quietly wear togas around campus.
They will wear a shirt all day that says, "Happy Bellybutton Appreciation Day!" and when anyone speaks to them they will ask, "Do you like my hat?" and then insist that they do have one on, even when people say they don't.
They will say, "in accordance with prophecy" after everything they say for 24 hours.
They will calculate the square root of 123,456 using the Babylonian method