The 15 biggest Friends plot holes and blunders fans can’t unsee – from changing sets to disappearing characters

FRIENDS is one of the most successful sitcoms of all time but it wasn't totally mistake free - there's plenty of silly blunders and plot holes it pick apart.

The iconic sitcom ran for a decade from 1994 to 2004 and it remains one of the most popular comedies on TV to this day.

It stars Jennifer Aniston, Courteney Cox, Lisa Kudrow, Matt LeBlanc, David Schwimmer and the late Matthew Perry as Rachel, Monica, Phoebe, Joey, Ross and Chandler.

Friends hits almost all of the right notes, that's what makes it so funny. But the show does make a few mistakes, too, whether that a character's outfit or appearance mysteriously changing or a storyline just blatantly contradiction something that's already been established.

Keep reading for a closer look at the 15 biggest blunders the show makes.

1. Chandler and Rachel forgot they already met

Throughout the course of Friends' ten season, Chandler and Rachel are introduced to each other for the first time on three separate occasions.

The first one these is during the pilot episode when a sopping wet and wedding-ready Rachel wanders into Central Perk looking for Monica. There Monica introduces her old school pal to her new friends, bar Ross, who Rachel already knows.

But viewers learn later that Rachel and Chandler actually spent multiple Thanksgivings together at the Gellers when they were younger, so it seems a bit odd that they forgot this in the pilot.

The same thing happens again when the gang fantasise what their lives would have been like if things worked out differently for them as adults. While Monica and Rachel were no longer friends in this alternate reality, surely Rachel and Chandler still would have remembered meeting at Thanksgiving?

2. Monica and Rachel's apartment door magically locks itself - but only once

Any Friends fans can tell you on one hand the number of times the door of Monica's apartment is locked, and that's usually because one of the characters has done it for a specific reason.

The door is never usually locked and open to all, hence why the gang spend so much time there. But in the first Thanksgiving episode, everyone ends up locked out of the apartment.

This happens because neither Monica or Rachel remember to take their keys with them - but this happens only once, since the door to the apartment doesn't normally lock itself.

3. The apartment number keeps changing

Talking of the magic apartment, the number on the door is another major blunder as seems to switch floors on a regular basis, at least in the early seasons…

When the show stars, Monica and Rachel live in apartment 1 with the guys across the hall at number 2. However, when the writers realised that they'd have to be on the ground floor for this to be logical they switched in to numbers 5 and 6 respectively.

However, this apparently still wasn't good enough and the numbers change again, this time from odd to even for Monica and Rachel's apartment which becomes number 20 - as it remains for the rest of the show.

4. Joey forgets how many sisters he has

Friends fans know that Joey comes from a very large family, but that he's the only boy among seven sisters - one of whom Chandler ended up making out with in series 3.

But in series 1 it seems Joey has forgotten about one of them because he remarks that he is one of seven siblings total. Although maths has never been Joey's strong suit, it's pretty hard to believe he'd just forget about his sisters, especially when he's so family orientated.

5. Joey's magic fridge

There is a particularly memorable episode of Friends in series six when a very broke Joey tries to blame the fact that his fridge has stopped working on anyone who steps foot in his apartment.

While Chandler eventually helps him out with the cost of a new fridge, Joey has to eat all the food inside it in the meantime, revealing as bit of a blunder.

The fridge door appears to open in both directions because when Rachel previously opened it, the hinges were on the left viewers you couldn't see what was in it, but it this episode it opens the other way.

6. Ross and Rachel's disappearing ink

The Vegas episode at the end of series 5 sets up one of the funniest Ross and Rachel storylines - the time they accidentally got married.

And it all starts with Ross drawing on Rachel's face in permanent marker while they're on the plane. When they learn that it won't come off for several days Ross feels terrible and lets Rachel draw on him, too.

However, the next morning as they deal with the fallout of accidentally getting married, the pen marks have completely disappeared from their faces.

7. No one knows when their birthdays are

The fact that none of the characters seem to know when their birthdays are is definitely one of the biggest, recurring plot holes in Friends.

It is established early on in the show that Joey is the youngest of the group. However, when Rachel's 30th birthday rolls around in series 7 it's revealed that everyone else had already turned 30, including Joey. It's a relief to learn that Ross has reached that milestone though because he remains 29-years-old for three seasons.

The confusion continues every time a character mentions their birthday as the dates and months change so frequently that anyone would have a hard time keeping up.

8. Monica and Chandler exchange their first 'I love you' twice

Monica and Chandler's relationship is one of the sweetest storylines in Friends, but even that is not without its issues.

The pair start sneaking around after Ross's failed wedding to Emily in London and date secretly for about six months before their friends find out.

During their secretive period, the couple have a fight that ends with Monica trying to cheer Chandler up by wearing a turkey on her head. Thrilled by the effort he says "I love you" to her for the first time.

Monica clearly hears him say this and does a celebratory dance, but a few episodes later, when all their friends find about them, she seems genuinely shocked to hear him say those three little words. It seems like a relationship milestone you would remember?

9. Rachel and Chandler's appearances drastically change in just a few hours

In romantic scenes at the end of series 6, Chandler pops the question to Monica, who excitedly accepts.

And in true Friends fashion, Rachel, Phoebe and Joey are waiting outside the door, so they are quickly called in so they can all celebrate.

Series 7 then picks up shortly after on the night of their engagement with the group planning to go get drinks at the Plaza to celebrate. However, it's hard not to notice that two of the characters have bene through major physical transformations.

Both Rachel and Chandler had dramatic haircuts over the course of the evening.

The reason for this was that there was actually a lengthy break between shooting the episodes, but obviously no one was thinking about continuity here.

10. What happened to Monica's wedding venue?

Monica finding her dream wedding venue was the catalyst event that led to Chandler proposing, but after all the drama around it, she didn't even end up using it.

It was a beautiful museum where Monica, Rachel and Phoebe went out to for lunch. Monica finds herself completely overcome and signs up to a two-year waiting list just in case. However, there ends up being a cancellation that means the Geller-Bing wedding can happen much sooner.

Did the couple just forget about this after they got engaged? Or did they just decide a long-engagement would be better? Either way, its never explained why they chose to get married in a hotel ballroom over the dreamy museum.

11. Rachel is pregnant for over a year

For years, Friends fans expected Monica to be the first of the three main female characters to become a mum - but in a shocking twist of events it turned out to be Rachel.

To add to the drama, Rachel finds out she's pregnant during Monica and Chandler's wedding reception, but won't reveal who the father is, although it's later revealed to be her ex-boyfriend Ross.

It's a long time before Rachel gives birth to her little one though. Too long, in fact. Since Chandler and Monica got married in May at which time Rachel was already six weeks pregnant, it should have been impossible for her to still be pregnant the following Valentine's Day - but what's a few extra weeks, right?

12. Ross forgets about his son

Ross definitely gets caught up in the excitement of having a new baby when Rachel finally gives birth to their daughter Emma, but he seems to have forgotten about his other child - his son Ben who he shares with ex-Carol.

Ben is born in series 1 and makes regular appearances during the early years of the show but soon disappears. In fact, he actually misses some major moments in his dad's life, like his wedding to Emily in London. And as far as fans know, Ben never even meets his new little sister. What on early happened to him?

13. Ross forgets losing his virginity

Apparently his son isn't the only thing Ross ends up forgetting. It's eventually revealed that Ross didn't actually lose his virginity with his ex-wife Carol as he had a sexual relationship with another woman at college before meeting her.

During an argument with Monica and Chandler, Ross reveals that his former college roommate got drunk and slept with their dorm cleaning lady, but Chandler quickly points out that was Ross.

This revelation changes everything viewers know about Ross' past, especially after he made such a big deal about her being his first back in series 1.

14. Chandler can't cry - except he can

In series 6, Monica makes a startling discovery about her husband-to-be; he can't cry. Chandler blames this on the circumstances of his childhood and its pretty much accepted by the group. They all seem to have forgotten that he's actually a very emotional person.

Phoebe has even witnessed Chandler's tears first hand. Back in series 3 she revels in the fact that she once made Chandler cry, and quite frankly he sobbed his heart out. And that doesn't seem like a moment you would forget anytime soon.

15. Rachel's magic key

Last but certainly not least on this list of blunders and plot holes is Rachel's magic apartment key in series 10.

Monica and Chandler get ready to serve up the show's last Thanksgiving, except everyone is late. In anger, Monica locks the door and puts the chain across, shutting out her friends when they do eventually arrive.

Rachel has the genius idea to use her old key which is coincidentally in Joey's apartment. She seems to have forgotten that when Monica and Chandler were away on their honeymoon that Joey wrecked their front door and had to have the locks changed.

Since Rachel moved out way before that, there's no way her old key would still work - and yet it does, unlocking the door just enough for the latecomers to make amends and enjoy Thanksgiving.