In a fantasy book called "Jack of Shadows" by Roger Zelazny I read this:
A disgraced member of a ruling party is being forced to ceremonially drink to the coronation of the new king, but instead defiantly lifts his cup, proclaims himself the new king, & drinks. Everyone else in the room pours their drink upon the floor.
Spilling wine on floors almost certainly wouldn't be acceptable in the present day, but the act makes me curious as to when it might have been commonplace & in what situations it might have been done. Disapproval of a wedding? A breakdown in negotiations between diplomats? A fight erupting amidst a dining hall?