It's a basic law of human nature: it's impossible to have a reasonable-sized wedding without some form of drama. It doesn't matter how happy the couple is, there will always be one drunk relative or wayward groomsman who makes it their job to bring the gossip.
When the relationship happens in less than perfect circumstances, this rule is doubly true. No matter how carefully you curate the guest list, the chances are that somebody will run their mouth at one point or another.
Sometimes, this can come from the people that you least expect. This seemed to be the case when one Redditor's brother had his second marriage, and found his sibling had something to say about the way in which it had come about. Not only had he cheated on his first wife with his new bride, his current partner had sent a number of offensive messages to his ex after the breakup. As someone who was fairly close to his ex wife, his brother saw fit to mention something about the situation in his speech. Then, all hell broke loose.
While not everyone may agree with the philosophy of "once a cheater, always a cheater", this guy definitely didn't do himself any favors. Not surprisingly, fellow Redditors were inclined to agree.
