While nobody outright said that saying the wrong name at the altar would be terrible, this reference to Friends, when Ross says Rachel instead of Emily at his wedding, summed it up beautifully.
Many people in the thread agreed that in addition to proposing, announcing an engagement or pregnancy is tacky and the worst thing to do at someone else’s wedding.
Several people suggested that fighting is the worst thing you can do at a wedding. One added that arguments are typical when you bring families together.