At a wedding, there are several cardinal sins a guest mustn't commit. Bringing a plus one without being offered the option is probably up there, as is showing up late to the ceremony. And of course, wearing white - the ultimate faux pas.
Perhaps even worse, wearing a white, midriff-baring crocheted top complete with a matching mini skirt - space buns à la the Spice Girls optional.
When presented with the aforementioned ensemble by her sister-in-law, one bride-to-be was left with no choice but to veto her idea of 'appropriate' wedding attire - but couldn't resist sharing a picture of the knitted nightmare to the popular Reddit forum, Wedding Shaming.
"My SIL [sister-in-law] just asked me if this was okay to wear to my wedding," the bride-to-be wrote, alongside a screenshot of the outfit in question - a white and red floral two-piece from the retail giant Target.
"Well, at least she asked, now you have an opportunity to veto it," a reader acknowledged, with the woman quickly replying: "Oh, I already did."
"I let her know that wearing white or any derivative of white is an absolute no from me dawg."
As it transpired, the two-piece being off-white was the least of its problems, with a number of readers jumping in to crucify the crocheted "abomination".
"I didn't even notice the white, I was so distracted by the fact that it was a crocheted crop top and mini skirt that looks like it came from Forever 21," a second observed, with a third adding: "As a crocheter, it's an abomination. If they really wanted to wear it, it comes in non-white colours."
"If they really wanted to wear it? I'm sure there's a beach-themed garden party or a pool party that SIL can wear it to instead," a fourth quipped.
"You maybe should have also mentioned that dressing like an adult is also a requirement," a fifth deadpanned.
"I'm sorry, it was the colour that's the problem? How about the fact that it looks like a pot holder on top and bottom. I would trade the colour issue for her wearing actual clothes."
"How old is she? Because that can take this from 'she should have enough common sense to know' to 'what the hell is she thinking'," another asked.
When the bride-to-be confirmed her sister-in-law is actually a 30-year-old, it only intensified the backlash.
"It's giving me 'toddler on a poolside family holiday' vibes, maybe with a hat in matching fabric. Either way, not appropriate for a wedding."
In a later comment, the woman clarified that her nuptials will be held on a beach, which may explain her sister-in-law's thinking.
"But come on, in what world is it okay to wear white to a wedding?" she reiterated.
"I don't think it's appropriate, even on a beach! There are so many pretty summer dresses and skirts available that would give a sense of occasion," another responded, with one agreeing: "Aside from the colour, this could be a reasonable outfit for a wedding held at a music festival or Burning Man or something like that.
"Otherwise, not even close to wedding wear."
Last month, one woman shared her predicament after she "accidentally" wore white to attend her cousin's 'surprise' wedding ceremony, much to her cousin's dismay - despite it being advertised as a christening.