Unless you're the one getting married, it's a faux pas to wear white to a wedding. It's rude; it upstages the bride; and it's supposedly bad luck. Plus, you're probably going to spill something on it (that last one might just be a me problem). Are there exceptions? Sure.
Maybe your house burned down leaving you with zero belongings but the white nighty you were wearing when you're house burned down, and you didn't have time to stop at TJ Maxx on the way to the wedding because you're already late because of your house burning down. That's the only one I can think of.
Apparently the bride's family felt differently, and called her out. And so did her boyfriend. So she went online, thinking strangers on Reddit would take her side, for some reason?
Spoiler alert: they did not.