Hm. This one's hard for me, because I rarely find myself disliking a TV romantic couple. Crichton/Aeryn grated on me at times, but nowhere near enough for me to peg it as one of my least favourites.
Er. Uh. Hm. Talia Winters/Susan Ivanova on B5. Not because they're both women, but Talia Winters was frankly always a rather obnoxious and annoying character, and paring her with probably the dullest human character wasn't a move I was that keen on. Well, it was short lived, hurrah.