The buck's and hen's nights that got so out of hand, the wedding was cancelled.

Here’s a hot tip: don’t cheat on your partner a couple of days before your wedding. It doesn’t bode well for the longevity of your relationship.

It might seem like straightforward advice, yet one of the leading causes of couple’s cancelling their impending nuptials mere moments before their big day appears to be bucks or hens night indiscretions.

Reddit users are sharing the bachelor and bachelorette party moments where it was obvious there wasn’t going to be a wedding afterwards.

Obviously, there are the cheaters:

“Bachelor hooks up with a girl, gives her his cell phone number so they can continue the party that night,” one recalls of a particularly raucous night out in Vegas.

“Bride to be is sitting at home with the iPad getting all of the iMessages from the girl. She cancelled the wedding that day.”

Ouch.

This can only end badly.

Another groom-to-be allegedly paid a stripper for a hand job, which led to his future brother-in-law punching him in the jaw. Quite rightly.

As one reader observed: "Who would be dumb enough to cheat on their soon to be wife in front of her brother?"

Good question.

Then there are the liars:

It's not just the boys who misbehave. One unfortunate groom discovered his future wife had been lying to him FOR THEIR ENTIRE RELATIONSHIP after a casual conversation between their respective sisters.

"Sister of the groom chatted with the sister of the bride. Just casual conversation but it came to light that almost 100% of what the bride had said besides her name was a complete lie," one person shared.

"Sister of the groom calls him up and says he really needs to figure out if this is right. A few fights and some long thinking later the groom leaves her and leaves town."

The drinkers:

"I was at a bachelor party the Tuesday night before a Saturday wedding," a bachelor party attendee recalled.

"After 8 hours or so of heavy drinking all day, we were at a baseball game and the groom punched a police officer in the back of the head and knocked him out for a few seconds. I watched it happen in slow motion, and thought to myself, "Welp, this wedding isn't going to be happening this weekend".

Mamamia staff share their biggest wedding day regrets. Post continues after video...

The straight-up crazies:

Some of the stories are actually just incredibly dark, so apologies in advance.

For example, the groom and best man who decided to kill the bride's ex-boyfriend.

"They did, they got caught, and the wedding was cancelled for obvious reasons," one man writes.

"As far as I know, the two are still serving time."

The ones that didn't happen during the bucks nor hens nights, but absolutely ruined relationships:

"A week before his wedding a friend of mine walked in on his dad having sex with his fiancée," one man writes.

"The next day in a fit of rage he trashed their room and in the process found explicit love letters between his recently married best friend (and best man) in her underwear drawer. The letters were as recent as the past week. The wedding was cancelled. Whenever I ran into him at a bar I made sure he never had to buy his own drinks."

At least he had one true friend, right? (Post continues after gallery.)

A hotel employee shared a very similar but gender-flipped tale in which the groom was caught with the mother-of-the-bride: