One of the most horrible ideas I grew up with had to do with making a matrimonial union official. It's a practice called consummation and the idea is that a couple has to have sex to make their marriage legitimate. The man must "take" the bride for her to "be his" in very fact. No sex, not a real marriage.
It's not a Mormon-born concept and I'm not sure if it counts as Mormon doctrine, but belief in it was alive and well in the Church during my formative years (but probably even more alive in the years Joseph Smith was prophet). My friends and I would sometimes talk about how soon after being sealed we were going to go consummate the marriage. Sometimes we would joke about doing it right away because we'd obviously be so horny right after the ceremony, but just as often we would choose the ASAP option because, according to our logic back then, you wouldn't want a terrible tragedy to happen and not have the marriage count. Either way, there was no time for delay.
Let's get some virgin blood on the sheets!