Bickering. It's not really conflict, they're just sniping at each other for no good reason. There's no believable motivation for the sniping. People just dislike each other on sight. And it's almost always followed by I-hate-you-but-I-can't-keep-my-hands-off-you-sex.
But wait, maybe this isn't the answer since the key phrase in this questions is books you actually enjoyed otherwise.
Once the couple starts bickering, the actually enjoyed otherwise part of the equation disappears. I can't enjoy sniping for the sake of comedy or someone's idea of sexual tension. Bickering isn't sexy or interesting or cool. It's childish and annoying.
But back to the actual question. Least favorite plot device overused in books I'd otherwise enjoy. Hmmmm.
[Tick-Tock. Tick-Tock. Check nails. Look at Twitter feed. Run to bathroom. Pour fresh Diet Coke into my glass . . .]
- Serial killers. So-o-o-o-o overdone and they all sound the same.
- The absence of conflict. Lots of thinking about the potential for conflict. Lots of posturing to avoid conflict, but no actual conflict. I recently read a book that fell into this category and I complained about it for days.
- Serial killers in books with no conflict, stalking bickering characters who repeatedly engage in I-hate-you-but-I-can't-keep-my-hands-off-you-sex!