The Ex-Fiancé
One of the worst things I’ve seen wasn’t even the bride; it was the groom’s baby mama/ex-fiancé who show up uninvited to the reception. She threw the wedding cake at the newly married couple before telling everyone how much of an absentee father he was.
After breaking a few wine bottles on the ground, she was restrained then arrested for assault with a weapon (wine bottle), assault, and destruction of private property. After that fiasco, the parents arranged for a private dinner for them and their bridal party.