As a wedding guest there are certain unwritten rules you should be aware of - don't forget to RSVP, put your phone on silent and arrive on time.
But unless you're the bride, wearing white to a wedding is considered the worst faux pas of all.
Unfortunately for one bride, one of her wedding guests didn't get the memo reported Daily Star.
The anonymous attendee turned up to the ceremony wearing a stunning floor-length lacy white gown - and it even featured a train.
The woman in question was called out on Reddit's Wedding Shaming forum where a number of users confused her for the bride.
A Facebook friend of hers wrote: "This girl looks absolutely gorgeous, stunning and every other word for perfect.
"But she is NOT the bride. You had one job..."
Since being posted it has received over 200 comments from people slamming her "inappropriate" outfit.
One person said: "Unreal, like does she not have a friend to perhaps suggest that, lovely though the gown might be, this is NOT the function to wear it to?
"Her bloke there must be up his own a** too or he might have noticed what she was wearing before they left the house and could have suggested she needed to rethink her aesthetic. Totally self-involved and selfish couple."
Another added: "It is considered extremely tacky to wear a white, gown like dress to a wedding. That honor should be reserved for the bride.
"Basically, it is the equivalent of yelling 'Look at me!' on one of the most important days of someone else's life."
Others said they would have asked the woman to leave if she turned up to their wedding wearing white.
With one saying: "If someone showed up in this to my wedding they’d be kicked out immediately."
And another agreeing: "Wear this to my wedding and I will personally toss you out."
Although the overriding response was that the woman was well and truly in the wrong, a couple of people didn't see what the problem was because the dress was actually ivory not white.
