Their wedding is an occasion when a bride and groom can reasonably expect for all the attention to be on them.
Stealing the newlyweds' thunder is considered a terrible faux pas.
• Read more: Ten rules of good wedding behaviour
And so it is unsurprising that a picture showing a wedding guest proposing to his girlfriend right in front of the bride and groom at their reception has been met with outrage and ridicule online.
The picture, uploaded to Reddit this week by an unnamed user who has since deleted their account, has been viewed a staggering 1.36million times.
More than 1,000 comments on the photograph are increasingly hilarious and scathing as community members air their disbelief at the unidentified guests' apparent rudeness.
The picture shows a newlywed couple, yet to be identified, smiling as a guest gets down on one knee to present a visibly emotional woman with an engagement ring.
The photo even shows that the guest had placed his bottle of beer on the table in front of the bride before getting down on one knee to propose to his girlfriend.
While the bride and groom appear to be happy with the events, the bride's arguably strained grin has been the subject of much discussion amongst Reddit commentators.
"Her smiles says 'congratulations', her eyes say 'that b**ch'," one user wrote.
"The bride is doing a really good job of hiding her murder," another added.
While Alliewonka added: "Honestly I feel kinda bad for the girl being proposed to more than the bride, she's being proposed to at someone else's big day, he hasn't made it personal for her at all but I guess she seems ok with it."
"Her smile pretends to be happy for them, but her eyes betray her true feelings," cry_wolf wrote.
And Hargbarglin wrote: "I feel like in some cases the people that would do something like this literally cannot deal with not being the center of attention."
It is unknown whether the bridal couple were aware the proposal was going to happen in the middle of their reception, or whether they gave their blessing.
Either way, the internet is outraged on their behalf.
Reddit users have helpfully come up with the perfect revenge, suggesting that the newlyweds announce that they are expecting at their friend's wedding - if they are indeed still friends.
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- Daily Mail