Rule number one... don't outshine the bride, right?
Your wedding day is a once-in-a-lifetime event (well... in some cases), so naturally the bride and groom should be the centre of attention all day.
And everyone knows the unspoken rules by now, don't wear white to the wedding, don't get too drunk at the reception and don't end up doing the worm on the dance floor at 2am.
However, one wedding guest for an upcoming ceremony is choosing to buck the unspoken rule...and it's causing real problems for the bride-to-be.
To make matters worse, that guest is the mother of the groom.
Taking to Reddit (the place where all frustrated brides to be go to vent) under the username lswo26, she asked people if she was being unreasonable over the situation.
She wrote: "My MIL just bought a dress to wear at my wedding. She did ask me beforehand what type of dress I think she should wear. I specifically told her to find something that is navy blue, dark green or grey and something conservative."
But the dress her mother-in-law purchased was anything but "conservative."
"It is gold with gold embellishments and gold threading. The whole dress is sparkly. When she showed it to me I was absolutely shocked and I wasn't very happy with her choice of dress. My dress in comparison is very simple with a little lace and some satin," she continued.
And it get worse, after the bride-to-be revealed the woman is planning an outfit change halfway through the reception into a second dress which is green, off the shoulder and covered in sequins.
The bride added: "Can you believe this woman?! I honestly can’t brain any of this as she’s an extremely simple woman who doesn’t even put effort to dress up on normal days.
"I did tell her in the most diplomatic way possible that her dress is not suitable for the function. She grabbed the dress out of my hands, stuffed it in the cupboard and gave me the silent treatment.
"I don't want to be mean as she might be going through a middle-age crisis and has high blood pressure."
Unsure of how to proceed she turned to her husband-to-be for help, but he merely claimed "all dresses looked the same to him."
Unsurprisingly, the online community was completely shocked by the mother-in-law's behaviour.
The dress the mother-in-law plans to wear to the weddingOne person commented: "You are not rocking the boat. She is rocking the boat. You're not overreacting at all- that is a literal wedding dress right there. She asked you what you wanted and went and did the exact opposite."
Another said: "Not overreacting at all. That's a wedding dress or a super fancy prom dress."
Many people suggested "accidentally" spilling red wine all over the dress and some even offered to do it for her.
''Time for a bottle of red wine in a large cup wielded by a good friend with lots of spine," posted a third.
"I’d be tempted to walk up to her at the reception and tell her everyone was talking about her poor taste in clothing and ask if she ran her dress choices by anyone. Because how embarrassing for her. I just thought she should know."
A fourth added: "You aren't being mean by pointing out that her dress was ridiculously unsuited to the event for someone in her role. It doesn't matter that she has high blood pressure. It doesn't matter that she thought she looked nice in a sleeveless dress twenty years ago. She isn't having a crisis, she's throwing a tantrum and giving you the silent treatment over a wildly inappropriate dress for your wedding . No way should that nonsense be tolerated or excused. She's middle-aged, which means she's had more than enough time to grow up. It's okay for you to set and enforce boundaries with her."
