For a character specifically written to be disliked, Janice is impressively likable in Friends - especially looking back at the show, and seeing how all the Friends gang treated her badly for years. A unique (and yes, annoying) laugh didn't deserve Chandler's constant break ups and reconnections, or just how much everyone in his social circle hated her. In fact, Janice is now often seen as one of the better characters - capable, caring, and just looking for a relationship.
Whatever the opinion is on Janice, though, it was clear from the start that she and Chandler were never a real option as a relationship. Despite constantly getting back together (or just meeting up again) throughout the show, all the red flags were there in the earliest seasons.
He Didn't Respect Her
ittedly, Chandler's sense of humor means that he makes mean jokes about everyone, including the people that he loves the most. But he was particularly bad about making fun of Janice, and this is just the start of the ways he shows how little he respects her. In the very first season, he invites her to a New Years Eve party because he doesn't want to be alone, and then dumps her at his friend's party, on New Years Eve. It was completely heartless, and showed how he just used her, rather than treating her like a human.
They Don't Communicate
At the start of Friends, Chandler is already trying to break up with Janice - which is also a clear sign of a doomed relationship! But what is worse is that when he tries to break things off, he can't manage it, and she always bursts into tears, causing him to stay with her out of guilt. Clearly, these two just can't communicate, and that's the bedrock of a relationship.
His Friends Hated Her
The rest of the Friends gang absolutely hated Janice, even though it was never really clear why, beyond finding her laugh annoying. Unreasonable as it was, though, the fact that Chandler's closest friends couldn't stand her was always going to be an issue.
This group is completely co-dependent and spend all their time together, every day. There's no way a relationship works here unless everyone is on board.
They Have Different Senses Of Humor
Chandler prides himself on being funny, even eventually going into marketing to try and make a career out of his sense of humor. And he is funny, even if his humor is often dry, sarcastic, and borderline mean. However, Janice has a totally different idea of what's funny, and seems to have a much more earnest, enthusiastic approach to life. For two people who find humor so important, the fact that they have a different idea of what that means is a big problem.
They're Only Together For Convenience
It's pretty quickly clear that both Janice and Chandler are with each other because it's convenient. At first, they end up dating because Chandler finds it harder to leave than to stay, and then because Chandler needs a NYE party date. Then, each time after this that they start dating it's because they have somehow just bumped into each other - on a blind date, online... they aren't rekindling their romance because they are making mature decisions to try again, but because someone familiar happened to show up nearby.
They Bring Out The Worst In Each Other
For all his quips, Chandler is quite insecure and doesn't want to make a scene or stand out in life. Janice, on the other hand, has no confidence issues. She loves being loud (and wearing loud clothes), and enjoys standing out and having fun. Together, this could work - she could bring him out of his shell and he could provide a steady influence, but in the show, it does the opposite.
Chandler visibly shrinks around her, and she seems to get even louder to compensate. He also seems meaner and more cowardly in how he treats her than he is with other women, and she seems willing to continue running back to him, acting without respect for herself. They can both do better.
She Is Clearly More Invested Than Him
From the start, it's clear that there's an imbalance in this dynamic, and that Janice is significantly more invested in the relationship than Chandler is. She is always willing to run back to him, and to be actively excited about restarting the relationship (and quite heartbreakingly hopeful, too). Having one person who is barely interested and another who is all in is never going to make for a healthy relationship.
She Never Stood Up To Him
It's clear from the woman who eventually became Chandler's wife that he was looking for an extremely strong, confident woman - and one who would stand up to him. Janice, despite being extremely outgoing and confident, rarely stood up to Chandler, and often made it clear she would just keep coming back. For better or worse, this is just not a dynamic that would work for Mr Bing.
He Actively Disliked Her
One of the biggest red flags (in a sea of red flags) is that Chandler never actually liked her - and he was constantly listing reasons to leave. Eventually, he did recognize that he was breaking up with women because of seemingly small flaws, and this even led to him getting back together with Janice, but it wasn't meant to be. In his eventual marriage, Chandler wasn't looking past Monica's flaws so that he wouldn't end up alone - he didn't even think about her flaws, he saw them as adorable quirks. Being with someone who he perceived as flawed and annoying was never going to last long-term.
The Timing Just Never Lined Up
Despite all this, many fans think that Chandler and Janice could have actually been soulmates - but they were doomed due to timing. When Chandler was first dating Janice, he just wasn't ready for a serious relationship. And by the time he was, he and Janice had so much history that it was never going to work. Perhaps this pair would have had a shot if she'd shown up halfway through the series, but we'll just never know.