I am lucky to say I've never witnessed a major crisis at a wedding. At the last wedding I attended, the mother of the bride walked around the reception telling the guests not to tip the bartender because "we already paid them," but that was more of a social faux pas than a catastrophe.
When I think of wedding disasters, I think of the Mitch and Cam wedding episode from Modern Family. Everything the writers could've come up with to go wrong went wrong. They had to break into the dry cleaners to get Cam's tux. Sal's water broke while she was officiating the ceremony. The venue almost burned to the ground because of wildfires. They had to evacuate the venue via school buses infested with monarch butterflies. Can y'all tell I was a big Modern Family head by how I can recall this without Googling the plot summary? It doesn't matter. What does matter is that former wedding guests took to Reddit to share stories of the worst things they've seen at weddings, and while they do not top sitcom absurdity, they are incredibly compelling.