I had a hard time dealing with Angel/Cordelia on Angel. It kinda felt like the writers just sorta slapped 'em together because they were the two highest billed characters of the opposite gender. (But then, I liked them together in "You're Welcome." I seem to only like Angel's relationships once they are over, like Angel/Buffy in "I Will Remember You.")
Of course, Cordelia/Connor on Angel was absolutely appalling. In the end, it was revealed that she wasn't really Cordelia anymore, but for some people, that doesn't make it any better.
On Torchwood, they dropped some Jack/Gwen hints early in the series. Then, the series suddenly made a very bizarre left turn when Gwen ended up having an affair with Owen for a couple episodes. That was just a bad move. It felt very mean-spirited, even for Torchwood. Thankfully, in Season 2 it seemed like the writers were content to forget that it ever happened. (Otherwise, I would have expected at least some awkwardness from Gwen or Owen when Owen first met Rhys.)
In the deliberately gross category: In the final episode of Arrested Development, after Lindsay discovered that she was not biologically related to Michael, she tried to seduce him in one of the most awkward, grossest attempted seductions in TV history.