Where so many Star Trek series were episodic, DS9 was the first to push the envelope and work off quite a few more several-episode stories. This mitigated the number of random adventures and made a lot of the storytelling so much more contained. There's no surprise that some people consider this series to be their favorite Trek.
However, even with less time for random episodes, DS9 still had enough time for some absurd romances. One-off relationships always scar fans with a vengeance, and, certainly, fans could never forget some of these rocky affairs.
Jake Sisko and Mardah
Okay, this relationship did last a couple of episodes. However, it wasn't talked about too much and was really, really weird. Jake Sisko, resident teenager and son of the station's Commander, was dating an adult woman. Yeah, it was kinda gross. Mardah seemed like a nice enough girl, but she was a Dabo girl hoping to go to university once she saved money. Until then, though, her several years older self was dating a young teen.
Considering Jake was probably only about 15 at the time and she was more like 19/20, it was a bit of an uncomfortable age gap. This was a pretty bad relationship, even if teenagers do sometimes date people totally wrong for their age.
Julian Bashir and Sarina Douglas
At first, Julian and Sarina were a little cute. He helped her brilliant mind get out of her head. Like the other genetically modified humans, she struggled with her place in the world. Now, she could speak and get involved in the world. However, not only did Julian seduce her away from her crush on the energetic Jack, but he also almost shut her down all over again. After all, the longer she spent with him, the further he pulled her from her family (the other modified humans).
Julian's pushiness was just way too pushy for Sarina. It would have been much better if she figured out how to get Jack to notice her in this episode. After all, she had feelings for him the time before that when fans saw her.
Elim Garak and Ziyal
Garak and Ziyal were a bizarre pairing. They had little explicit romantic moments, but the romance that did happen was mismatched. It makes sense that Ziyal might get a crush on the only person who looked anything like her, but the fact it went anything further than friendship is bizarre. Ziyal was only a very young adult and Garak was a grown man with years of violent experience under his belt.
A forbidden romance between her and Jake Sisko would have made so much more sense. He would be more open-minded than other Bajorans, he was her age, and they both would understand each other. But, guess her and Garak was a better idea? (Not really).
Kira Nerys and Thomas Riker
One of the weirdest thing Star Trek has ever done is have a Riker clone floating around the universe. Even weirder was having him turn into a terrorist and have a flirtation with Major Kira Nerys. Weirder is having them kiss after she figures out he's a terrorist and right before he turned himself over to Cardassian forces (a.k.a. they probably executed him).
The whole episode feels enough like a fever dream, but to think any version of the wild Riker attracted the powerful ex-resistance member with a temper, who normally would break men's fingers for being too flirty, feels a bit absurd. Between the ending and the logic of it, let's just chalk it up to a bad relationship that only happened because people liked Riker and Ro together once upon a time.
Odo and The Female Changeling
Yuck. While there are a lot of bad relationships here, let's start this one off with disgust. The changeling way of exchanging information is kinda confusing, considering it's been compared to a friendly bond... and also sex. But Odo's melding with The Female Changeling is by far the worst. She spent the whole time seducing him and manipulating with her own cells.
Yeah, Star Trek's own rigid Odo was almost brought to the Dominion dark side just because of the promise of mind-blowing sex. This whole relationship moment just makes fans feel gross. Let's prefer to pretend it didn't happen.
Quark and Pel
Oh Quark, what a fickle Ferengi. So, Quark meets this fantastic, business-minded waiter. Only problem? They are actually a female named Pel masquerading as a man to get into the business world. Unlucky for her, though, she falls in love with Quark. Pel was bold, intelligent, and brave. However, Quark turned her down because he said that he preferred meek women who will come to his every beck and call, as Ferengi customs encourage.
Every fan knows that Quark is a dirty liar. His other romances/loves have all been with other bold, powerful, not at all meek women. Grilka, Jadzia, Natima. They were all so intelligent and fearless. Pel was totally his type, Quark is just being oblivious to his own feelings. This relationship was so disappointing.
Jadzia Dax and Deral
Pretty early on in the series, Jadzia had one of the infamous "single episode soulmate" experiences. Ya'see, Star Trek does that sometimes where a character will be so in love with someone that they might leave Starfleet and their friends forever. But, of course, at the end of the episode, they don't.
Well, say hello to Deral. He is a member of a colony trapped on a planet that fades in and out of time. They appear for a week or so in space and then disappear for years. What a temporal anomaly.
Well, this spotted man wants to leave the planet to be with her, but when he can't leave, she plans on joining his colony. But then they fade out of time without her because she doesn't belong. Rough break, but the relationship was pretty lukewarm, excluding one comment about counting each others' spots.
Nog and Varis Sul
Ferengi aren't known for being the most respectful to women. Arguably, they're known to be pretty terrible and misogynistic and rude. So, when Nog gets a crush on Varis Sul, a young woman fighting for her family's land rights, it gets weird. He offends her, keeps on pushing his way into her life, and, if it hadn't been for Jake being a constant great guy, she never would've seen any good side of him.
The fact this little crush gives Nog a kiss on the cheek despite him not really learning anything about being better to girls is pretty brutal. Varis was cute and deserved better. It would've been great if Nog really learned something from this, but alas.
Worf and Grilka
Between being way too serious of a Klingon and a serial half-Klingon/Klingon sympathizing dater, full-blooded, hardcore Klingon women aren't exactly Worf type. Don't dare tell Worf that, though.
The second the poor guy sees Grilka, a perfect specimen of Klingon, he falls head over heels and is determined to win her heart. Problem? She has zero interest in him. Having to watch him moon over someone so wrong for him was exhausting. He needs someone patient with his misinterpreted Klingon-ism. Grilka definitely wouldn't be.
But, oh well, guess this bad flirtation get married in some of the books? Yeah, dude deserves something different.
Kira Nerys and Gul Dukat
Ah yes, the top of the terrible DS9 flirtations. While the series never officially tried to make Kira and Dukat a thing, they constantly hinted at his attraction to her and her possible attraction to him. Well, in earlier seasons. Later she aggressively shuts him down and it's great.
But, before that, even hinting she may like him? A guy who decimated thousands of her people, executed her fellow resistance members, and took Bajoran woman as his sexual playthings? Absolutely not. That's a horrible relationship to even imply could happen. Do not act like they're your divorced parents, Ziyal, that's gross. Better to pretend this whole thing never happened.