Watergate
From Memory Alpha, the free Star Trek reference.
"Watergate" was a political scandal in the 1970s that forced Richard M. Nixon to resign as President of the United States.
In 2369, Q told Vash that, along with the Crusades and the Spanish Inquisition, he believed Watergate to be one of the most interesting events to happen on Earth. (DS9: "Q-Less")
