PISS INTO THE WEDDING CAKE

{v. phr.}, {vulgar}, {avoidable} To spoil someone's pleasure or celebration by doing or saying something harsh or unseemly in an otherwise happy gathering; bring up depressing or unhappy subjects at a supposedly happy time. * /Stuart really spit into the wedding cake when he told Burt in a bragging fashion that Lucy, Burl's bride, used to be his girlfriend./