Anything where the wedge between the lovers is contrived and makes them look like dolts. This is so common that I could type my fingers bloody listing examples, but here's a few:
Ezri/Bashir/Worf love triangle - maintained by the writers only by the expedient of making the characters act like they're in the fourth grade.
Chuck/Sarah - if the writers are playing fair with
then there should be no obstacle to Chuck and Sarah hooking up. If the writers contrive another obstacle this season, it had better be a good one. Why can't they just forgo the UST and let them have sex, if that's what's natural for the plot?