Every Friends fan will claim to know that Ross and Rachel were endgame from the start - after all, he's her lobster! But most of the relationships on the show were a little more of a mystery. No one knew if Monica would end up with Chandler or Richard until the moment of her proposal (and even then, some fans felt she made the wrong choice). No one expected that a blind date Joey found for Phoebe by calling out a name in a crowded coffee house would lead to her wedding day.
And while some relationships managed to surprise viewers, and others were clearly going to be the biggest ships of the show, there are a few that every fan knew would end in tears. These are the dates and couples that were doomed from the start - and everyone, except the people involved, knew it.
Rachel & Paolo
When Rachel was exploring her new freedom in the city, figuring out how to date after running out on her wedding, she met Paolo. The two had absolutely nothing in common - not even a language - and it was abundantly clear that Rachel was simply involved with him because she wanted to have a wild fling with a sexy guy. She even said as much, although she did start to wonder after a while if it could go further... she was the only one wondering, though. Every fan knew that by that point, Ross was being set up as her one-and-only, and Paolo was just a gorgeous jerk.
Chandler & Kathy
In some ways, Chandler and Kathy seemed perfect for each other. They got along wonderfully, they had real chemistry and connection, they cared about each other... but of course, there was one major problem that doomed this pair from the very start: Kathy was Joey's girlfriend. The two didn't have much between them, of course, and Kathy was much better suited to a relationship with Chandler, but they cheated on Joey - and given how close Joey and Chandler are (and how insecure Chandler is), this was always going to spell the end for them.
Joey & Charlie
In the later seasons, Joey got into a few relationships that just didn't seem to make any sense. Fans largely hated his pairing with Rachel, and before that, there was his brief thing with Charlie.
It was clear that this wasn't going to go anywhere from the moment that Charlie suggested going to the Met (the museum) and Joey corrected her, saying it was the 'Mets' (the sports team). These two were just on completely different wavelengths.
Phoebe & Parker
Parker and Phoebe only dated for two episodes, but he's one of her more memorable romances. At first, he just seems like a charming guy, but it is soon clear that his positivity is painfully abrasive, and even for Phoebe, it's too much (especially after the rest of the gang make fun of him for it). This was a great little gag character, but it was clear from how over the top he was that it was only ever meant to be a short-term thing.
Monica & Pete
Monica and Pete actually seemed to have a decent shot at things for a while, and he was one of her more serious relationships on the show. However, despite the fact that it got far enough that Monica actually thought he was going to propose, it was clear that this wasn't going to happen. For one thing, their 'meet cute' was just plain problematic, as he essentially wore her down, and attempted to pay her to date him (trying to be cute about it, but still - when put plainly, it doesn't sound good). For another thing, he was a millionaire. And while there's nothing wrong with dating a rich man, that just wasn't going to be the storyline for a character in a sitcom about being 'broke' in New York City.
Phoebe & Eric
Dating a friend's ex can get complicated. Dating a sibling's ex, even more so. But dating the ex of a twin, after being the one to break them up? Of course this relationship was never going to work. Phoebe and Eric would have otherwise been a really sweet couple, as he was a caring, considerate man, and Phoebe did the right thing letting him know that Ursula was lying to him about basically everything. If they had met in other circumstances, this could have really worked, but as it was, they just couldn't get past the weirdness... especially after Ursula came over and slept with him, pretending to be Phoebe.
Chandler & Nina
There are quite a few problematic boss/employee (and teacher/student) relationships in Friends, and it was clear from the start that none of them would go the distance. Rachel admitted to 'hiring herself a treat' when she gave Tag an assistant job, and obviously that was going to be a problem. Ross knew from the start that he could lose his job for dating Elizabeth, as she was his student.
And Chandler not only dated his subordinate, Nina, he refused to fire her as part of layoffs, and made up stories about her being 'crazy' in order to explain it to his boss. This was a terrible storyline no matter how fans looked at it.
Ross & Janice
Janice may be one of the most underrated exes on Friends, as she was actually a pretty great person, who got consistently treated terribly by Chandler - but every fan knew that her relationship with Ross would never make it. The two ended up bonding over their various divorces, much to Chandler's shock (despite the fact that he himself dated her on and off for years) - but the only surprise when it ended was that Janice was the one to break up with Ross.
Rachel & Joshua
This is another relationship that had some potential - but also came with a lot of warning flags. The main issue was that Rachel and Joshua just weren't on the same level when it came to interest; Rachel was pining over Joshua, while he clearly just saw her as someone he was working with (as she was his personal shopper). He missed all the clues that she wanted to date him, and it's a wonder they even got to that point, let alone lasting beyond it.
Joey & Janine
Joey's roommate search, and his relationship with Janine, had issues from the start - especially when Joey's first ad for a roommate included the limitations 'non-smoker, non-ugly'. He then chose Janine as a roommate based solely on her appearance, in the hopes that he would be able to date her. And while that actually happened (after a while), this was never going to last. For one thing, Joey was constantly obsessing over how 'hot' she was, and for another, they didn't actually seem to have anything in common. The way it ended (when Janine revealed that she hated Monica and Chandler) may have come as a surprise, but the end itself didn't.