Buffy/Angel I hated Angel from the begining, this relationship was doomed from the start and it was like watching paint dry. I always thought Buffy/Spike had more energy.
I think Buffy had uniformly terrible taste in men. Buffy/Angel, Buffy/Riley, & Buffy/Spike were all terrible for different reasons. Buffy/Angel didn't work because while Angel was on Buffy
he didn't have any real personality. He was just the hunky vampire for Buffy & Cordelia to drool over. Buffy & Riley just plain didn't have any chemistry (although I think that Riley is an underrated member of the Scooby gang). And while there was a very interesting, explosive chemistry between Buffy & Spike, the whole attempted rape at the end of Season 6 made it all too unseemly. Personally, I'm a Buffy/Xander 'shipper.
Another vote for Battlestar Galatica
's "quadrangle of doom"-- Sam Anders/Starbuck/Apollo/Dee. Starbuck was a contemptible, selfish bitch who did nothing but jerk around all the men in her life. Apollo was an empty headed doormat. I don't see how any women were attracted to him. And I don't think any of us ever forgave Dee for ditching Billy.
I'm also not a big fan of these patriarch/matriarch romances like Bill Adama/Laura Roslin on Battlestar Galactica
or Captain Janeway/Chakotay on Star Trek: Voyager.
Tara/Willow: 1) Because Willow is straight, and no amount of retconning by Whedon will convince me other wise and
2)Because how the hell do you make two chicks making out boring.
I don't necessarily have a problem with making Willow a lesbian. However, I wish the show had given us an in-show way to reconcile that with Willow's obvious feelings for Xander & Oz in the earlier seasons.
I agree it's stunning how boring the Willow/Tara romance was. I did find myself intrigued by some of the Willow/Fred possibilities in "Orpheus." And I often felt that a Dawn/Tara romance would be very interesting. But Willow/Tara just totally falls flat.
Chakotay/Seven - Came from absolutely nowhere right at the end of the series, it was more of a distraction than anything else in the finale with them trying to put some sort of relevance on a relationship that the audience was not invested in at all.
I'm surprised I didn't think of this one. Actually, I'm glad I didn't think of it. That means this horrible idea is slowly fading from my memory. (Now, if only I could forget about the Kes/Neelix thing too.)
Rodney McKay/Jennifer Keller from Stargate Atlantis - I liked the Katie Brown/Rodney relationship better. There was more chemestry between them.
I didn't like Katie Brown. Whenever she was around, it made Rodney act like an idiot. Rodney is far less stupid when he's around Keller. (But then, I haven't seen Season 5 yet, so my exposure to this relationship is limited.)